diff --git a/gc.c b/gc.c
index 6fdf7f82..0c0e57f4 100644
--- a/gc.c
+++ b/gc.c
@@ -451,6 +451,7 @@ char *gc_copy_obj(object dest, char *obj, gc_thread_data * thd)
       memcpy(s, string_str(obj), string_len(obj) + 1);
       mark(hp) = thd->gc_alloc_color;
       type_of(hp) = string_tag;
+      string_num_cp(hp) = string_num_cp(obj);
       string_len(hp) = string_len(obj);
       string_str(hp) = s;
       return (char *)hp;
diff --git a/include/cyclone/runtime.h b/include/cyclone/runtime.h
index 6a8027dd..80ea3f87 100644
--- a/include/cyclone/runtime.h
+++ b/include/cyclone/runtime.h
@@ -194,6 +194,7 @@ int binstr2int(const char *str);
 int octstr2int(const char *str);
 object Cyc_string_append(void *data, object cont, int argc, object str1, ...);
 object Cyc_string_length(void *data, object str);
+object Cyc_string_byte_length(void *data, object str);
 object Cyc_substring(void *data, object cont, object str, object start,
                      object end);
 object Cyc_string_ref(void *data, object str, object k);
@@ -707,4 +708,27 @@ void add_global(object * glo);
 void Cyc_set_globals_changed(gc_thread_data *thd);
 /**@}*/
 
+/**
+ * \defgroup prim_utf8 UTF-8
+ *
+ * @brief Unicode processing using UTF-8
+ */
+/**@{*/
+#define CYC_UTF8_ACCEPT 0
+#define CYC_UTF8_REJECT 1
+
+/**
+ * Simple macro to make it more convenient to convert a single char
+ */
+#define Cyc_utf8_encode_char(dest, dest_size, char_value) \
+  Cyc_utf8_encode(dest, dest_size, &char_value, 1)
+
+int Cyc_utf8_encode(char *dest, int sz, uint32_t *src, int srcsz);
+uint32_t Cyc_utf8_decode(uint32_t* state, uint32_t* codep, uint32_t byte);
+int Cyc_utf8_count_code_points(uint8_t* s);
+int Cyc_utf8_count_code_points_and_bytes(uint8_t* s, char_type *codepoint, int *cpts, int *bytes);
+uint32_t Cyc_utf8_validate_stream(uint32_t *state, char *str, size_t len); 
+uint32_t Cyc_utf8_validate(char *str, size_t len);
+/**@}*/
+
 #endif                          /* CYCLONE_RUNTIME_H */
diff --git a/include/cyclone/types.h b/include/cyclone/types.h
index 647f4ba3..65dc2d99 100644
--- a/include/cyclone/types.h
+++ b/include/cyclone/types.h
@@ -465,6 +465,12 @@ void clear_mutations(void *data);
 /** Minimum allowed value of a fixnum */
 #define CYC_FIXNUM_MIN -1073741824
 
+/**
+ * Explicit character type now that we are using UTF-8.
+ * Chars are still value types though
+ */
+typedef uint32_t char_type;
+
 /**
  * Determine if an object is an integer.
  */
@@ -488,12 +494,12 @@ void clear_mutations(void *data);
 /**
  * Convert from an object to a char.
  */
-#define obj_obj2char(x) (char)((long)(x)>>2)
+#define obj_obj2char(x) (char_type)((uintmax_t)(x)>>2)
 
 /**
  * Convert from a char to an object.
  */
-#define obj_char2obj(c) ((void *)((((unsigned long)c)<<2) | 2))
+#define obj_char2obj(c) ((void *)((((uintmax_t)c)<<2) | 2))
 
 /**
  * Is the given object a value type?
@@ -721,16 +727,21 @@ typedef enum {
 typedef struct {
   gc_header_type hdr;
   tag_type tag;
+  int num_cp;
   int len;
   char *str;
 } string_type;
 
+// TODO: below macros are obsolete, need new ones that populate num_cp and
+// raise an error if an invalid UTF-8 char is detected
+
 /** Create a new string in the nursery */
 #define make_string(cs, s) string_type cs; \
 { int len = strlen(s); \
   cs.hdr.mark = gc_color_red; \
   cs.hdr.grayed = 0; \
   cs.tag = string_tag; \
+  cs.num_cp = len; \
   cs.len = len; \
   cs.str = alloca(sizeof(char) * (len + 1)); \
   memcpy(cs.str, s, len + 1);}
@@ -744,6 +755,7 @@ typedef struct {
   cs.hdr.mark = gc_color_red; \
   cs.hdr.grayed = 0; \
   cs.tag = string_tag; cs.len = len; \
+  cs.num_cp = len; \
   cs.str = alloca(sizeof(char) * (len + 1)); \
   memcpy(cs.str, s, len); \
   cs.str[len] = '\0';}
@@ -755,9 +767,51 @@ typedef struct {
 #define make_string_noalloc(cs, s, length) string_type cs; \
 { cs.hdr.mark = gc_color_red; cs.hdr.grayed = 0; \
   cs.tag = string_tag; cs.len = length; \
+  cs.num_cp = length; \
   cs.str = s; }
 
-/** Get the length of a string */
+/** Create a new string in the nursery */
+#define make_utf8_string(data, cs, s) string_type cs; \
+{ int len = strlen(s); \
+  cs.hdr.mark = gc_color_red; \
+  cs.hdr.grayed = 0; \
+  cs.tag = string_tag; \
+  cs.num_cp = Cyc_utf8_count_code_points((uint8_t *)s); \
+  if (cs.num_cp < 0) { \
+    Cyc_rt_raise_msg(data, "Invalid UTF-8 characters in string"); \
+  } \
+  cs.len = len; \
+  cs.str = alloca(sizeof(char) * (len + 1)); \
+  memcpy(cs.str, s, len + 1);}
+
+/** 
+ * Create a new string with the given length 
+ * (so it does not need to be computed) 
+ */
+#define make_utf8_string_with_len(cs, s, length, num_code_points) string_type cs;  \
+{ int len = length; \
+  cs.hdr.mark = gc_color_red; \
+  cs.hdr.grayed = 0; \
+  cs.tag = string_tag; cs.len = len; \
+  cs.num_cp = num_code_points; \
+  cs.str = alloca(sizeof(char) * (len + 1)); \
+  memcpy(cs.str, s, len); \
+  cs.str[len] = '\0';}
+
+/**
+ * Create a string object using the given C string and length.
+ * No allocation is done for the given C string.
+ */
+#define make_utf8_string_noalloc(cs, s, length) string_type cs; \
+{ cs.hdr.mark = gc_color_red; cs.hdr.grayed = 0; \
+  cs.tag = string_tag; cs.len = length; \
+  cs.num_cp = length; \
+  cs.str = s; }
+
+/** Get the length of a string, in characters (code points) */
+#define string_num_cp(x) (((string_type *) x)->num_cp)
+
+/** Get the length of a string, in bytes */
 #define string_len(x) (((string_type *) x)->len)
 
 /** Get a string object's C string */
diff --git a/mstreams.c b/mstreams.c
index f1b1c50e..939d4047 100644
--- a/mstreams.c
+++ b/mstreams.c
@@ -102,6 +102,7 @@ void Cyc_io_get_output_string(void *data, object cont, object port)
   }
   {
     make_string_with_len(s, p->str_bv_in_mem_buf, p->str_bv_in_mem_buf_len);
+    s.num_cp = Cyc_utf8_count_code_points((uint8_t *)string_str(&s));
     return_closcall1(data, cont, &s);
   }
 }
diff --git a/runtime.c b/runtime.c
index 1525f2d0..9b9e09af 100644
--- a/runtime.c
+++ b/runtime.c
@@ -181,6 +181,7 @@ void pack_env_variables(void *data, object k)
     svar->str = alloca(sizeof(char) * (svar->len));
     strncpy(svar->str, e, svar->len);
     (svar->str)[svar->len] = '\0';
+    svar->num_cp = Cyc_utf8_count_code_points((uint8_t *)svar->str);
 
     if (eqpos) {
       eqpos++;
@@ -189,6 +190,7 @@ void pack_env_variables(void *data, object k)
     sval->hdr.grayed = 0;
     sval->tag = string_tag; 
     sval->len = strlen(eqpos);
+    svar->num_cp = Cyc_utf8_count_code_points((uint8_t *)eqpos);
     sval->str = eqpos;
     set_pair(tmp, svar, sval);
     set_pair(p, tmp, NULL);
@@ -558,7 +560,7 @@ void Cyc_rt_raise(void *data, object err)
 
 void Cyc_rt_raise2(void *data, const char *msg, object err)
 {
-  make_string(s, msg);
+  make_utf8_string(data, s, msg);
   make_pair(c3, err, NULL);
   make_pair(c2, &s, &c3);
   make_pair(c1, boolean_f, &c2);
@@ -571,7 +573,7 @@ void Cyc_rt_raise2(void *data, const char *msg, object err)
 
 void Cyc_rt_raise_msg(void *data, const char *err)
 {
-  make_string(s, err);
+  make_utf8_string(data, s, err);
   Cyc_rt_raise(data, &s);
 }
 
@@ -802,7 +804,10 @@ object Cyc_display(void *data, object x, FILE * port)
     return quote_void;
   }
   if (obj_is_char(x)) {
-    fprintf(port, "%c", obj_obj2char(x));
+    char cbuf[5];
+    char_type unbox = obj_obj2char(x);
+    Cyc_utf8_encode_char(cbuf, 5, unbox);
+    fprintf(port, "%s", cbuf);
     return quote_void;
   }
   if (obj_is_int(x)) {
@@ -982,7 +987,7 @@ static object _Cyc_write(void *data, object x, FILE * port)
     return quote_void;
   }
   if (obj_is_char(x)) {
-    char c = obj_obj2char(x);
+    char_type c = obj_obj2char(x);
     switch (c) {
     case 0:   fprintf(port, "#\\null"); break;
     case 7:   fprintf(port, "#\\alarm"); break;
@@ -993,11 +998,13 @@ static object _Cyc_write(void *data, object x, FILE * port)
     case 27:  fprintf(port, "#\\escape"); break;
     case 32:  fprintf(port, "#\\space"); break;
     case 127: fprintf(port, "#\\delete"); break;
-    default:
-      fprintf(port, "#\\%c", obj_obj2char(x));
+    default: {
+      char cbuf[5];
+      Cyc_utf8_encode_char(cbuf, 5, c);
+      fprintf(port, "#\\%s", cbuf);
       break;
+      }
     }
-    //fprintf(port, "#\\%c", obj_obj2char(x));
     return quote_void;
   }
   if (obj_is_int(x)) {
@@ -1095,7 +1102,10 @@ object Cyc_write_char(void *data, object c, object port)
   if (obj_is_char(c)) {
     FILE *fp = ((port_type *) port)->fp;
     if (fp){
-      fprintf(fp, "%c", obj_obj2char(c));
+      char cbuf[5];
+      char_type unbox = obj_obj2char(c);
+      Cyc_utf8_encode_char(cbuf, 5, unbox);
+      fprintf(fp, "%s", cbuf);
     }
   } else {
     Cyc_rt_raise2(data, "Argument is not a character", c);
@@ -1816,7 +1826,7 @@ object Cyc_symbol2string(void *data, object cont, object sym)
   Cyc_check_sym(data, sym);
   {
     const char *desc = symbol_desc(sym);
-    make_string(str, desc);
+    make_utf8_string(data, str, desc);
     _return_closcall1(data, cont, &str);
 }}
 
@@ -1833,21 +1843,44 @@ object Cyc_string2symbol(void *data, object str)
 
 object Cyc_list2string(void *data, object cont, object lst)
 {
-  char *buf;
-  int i = 0;
-  object len;
+  char *buf, cbuf[5];
+  int i = 0, len = 0;
+  object cbox, tmp = lst;
+  char_type ch;
 
   Cyc_check_pair_or_null(data, lst);
-  len = Cyc_length(data, lst);  // Inefficient, walks whole list
+
+  // Need to walk the list of chars to compute multibyte length
+  while (tmp) {
+    if (is_value_type(tmp) || ((list) tmp)->tag != pair_tag) {
+      Cyc_rt_raise2(data, "length - invalid parameter, expected list", tmp);
+    }
+    cbox = car(tmp);
+    ch = obj_obj2char(cbox);
+    if (!obj_is_char(cbox)) {
+      Cyc_rt_raise2(data, "Expected character but received", cbox);
+    }
+    if (!ch) {
+      len++;
+    } else {
+      Cyc_utf8_encode_char(cbuf, 5, ch);
+      len += strlen(cbuf);
+    }
+    tmp = cdr(tmp);
+  }
 
   {
-    make_string_noalloc(str, NULL, (obj_obj2int(len)));
-    str.str = buf = alloca(sizeof(char) * (obj_obj2int(len) + 1));
+    make_string_noalloc(str, NULL, len);
+    str.str = buf = alloca(sizeof(char) * (len + 1));
     while ((lst != NULL)) {
-      if (!obj_is_char(car(lst))) {
-        Cyc_rt_raise2(data, "Expected character but received", car(lst));
+      cbox = car(lst);
+      ch = obj_obj2char(cbox); // Already validated, can assume chars now
+      if (!ch) {
+        i++;
+      } else {
+        Cyc_utf8_encode_char(&(buf[i]), 5, ch);
+        i += strlen(buf+i);
       }
-      buf[i++] = obj_obj2char(car(lst));
       lst = cdr(lst);
     }
     buf[i] = '\0';
@@ -2032,7 +2065,7 @@ object Cyc_string_cmp(void *data, object str1, object str2)
 }
 
 #define Cyc_string_append_va_list(data, argc) { \
-    int i = 0, total_len = 1; \
+    int i = 0, total_cp = 0, total_len = 1; \
     int *len = alloca(sizeof(int) * argc); \
     char *buffer, *bufferp, **str = alloca(sizeof(char *) * argc); \
     object tmp; \
@@ -2041,6 +2074,7 @@ object Cyc_string_cmp(void *data, object str1, object str2)
       str[i] = ((string_type *)str1)->str; \
       len[i] = string_len((str1)); \
       total_len += len[i]; \
+      total_cp += string_num_cp((str1)); \
     } \
     for (i = 1; i < argc; i++) { \
       tmp = va_arg(ap, object); \
@@ -2048,6 +2082,7 @@ object Cyc_string_cmp(void *data, object str1, object str2)
       str[i] = ((string_type *)tmp)->str; \
       len[i] = string_len((tmp)); \
       total_len += len[i]; \
+      total_cp += string_num_cp((tmp)); \
     } \
     buffer = bufferp = alloca(sizeof(char) * total_len); \
     for (i = 0; i < argc; i++) { \
@@ -2056,6 +2091,7 @@ object Cyc_string_cmp(void *data, object str1, object str2)
     } \
     *bufferp = '\0'; \
     make_string(result, buffer); \
+    string_num_cp((&result)) = total_cp; \
     va_end(ap); \
     _return_closcall1(data, cont, &result); \
 }
@@ -2076,6 +2112,12 @@ object Cyc_string_append(void *data, object cont, int _argc, object str1, ...)
 }
 
 object Cyc_string_length(void *data, object str)
+{
+  Cyc_check_str(data, str);
+  return obj_int2obj(string_num_cp(str));
+}
+
+object Cyc_string_byte_length(void *data, object str)
 {
   Cyc_check_str(data, str);
   return obj_int2obj(string_len(str));
@@ -2083,8 +2125,10 @@ object Cyc_string_length(void *data, object str)
 
 object Cyc_string_set(void *data, object str, object k, object chr)
 {
+  char buf[5];
   char *raw;
-  int idx, len;
+  int idx, len, buf_len;
+  char_type input_char;
 
   Cyc_check_str(data, str);
   Cyc_check_num(data, k);
@@ -2093,12 +2137,82 @@ object Cyc_string_set(void *data, object str, object k, object chr)
     Cyc_rt_raise2(data, "Expected char but received", chr);
   }
 
+  input_char = obj_obj2char(chr);
+  if (!input_char) {
+    buf_len = 1;
+  } else {
+    Cyc_utf8_encode_char(buf, 5, input_char);
+    buf_len = strlen(buf);
+  }
+
   raw = string_str(str);
   idx = unbox_number(k);
   len = string_len(str);
 
   Cyc_check_bounds(data, "string-set!", len, idx);
-  raw[idx] = obj_obj2char(chr);
+
+  if (string_num_cp(str) == string_len(str) && buf_len == 1) {
+    // Take fast path if all chars are just 1 byte
+    raw[idx] = obj_obj2char(chr);
+  } else {
+    // Slower path for UTF-8, need to handle replacement differently 
+    // depending upon how the new char affects length of the string
+    char *tmp = raw, *this_cp = raw;
+    char_type codepoint;
+    uint32_t state = 0;
+    int i = 0, count, prev_cp_bytes = 0, cp_idx;
+
+    // Find index to change, and how many bytes it is
+    for (count = 0; *tmp; ++tmp){
+      prev_cp_bytes++;
+      if (!Cyc_utf8_decode(&state, &codepoint, (uint8_t)*tmp)){
+        if (count == idx) {
+          break;
+        }
+        this_cp = tmp + 1;
+        count += 1;
+        prev_cp_bytes = 0;
+      }
+      i++;
+    }
+    cp_idx = i;
+    if (state != CYC_UTF8_ACCEPT) {
+       Cyc_rt_raise2(data, "string-set! - invalid character at index", k);
+    }
+
+    // Perform actual mutation
+    //
+    // Now we know length of start (both in codepoints and bytes),
+    // and we know the codepoint to be replaced. by calculating its length
+    // we can compute where the end portion starts, and by using str we can
+    // figure out how many remaining bytes/codepoints are in end
+    //
+    // 3 cases: 
+    // - 1) buf_len = prev_cp_bytes, just straight replace
+    if (buf_len == prev_cp_bytes) {
+      for (i = 0; i < buf_len; i++) {
+        this_cp[i] = buf[i];
+      }
+    }
+    // - 2) buf_len < prev_cp_bytes, replace and shift chars down
+    else if (buf_len < prev_cp_bytes) {
+      // Replace code point with shorter one
+      for (i = 0; i < buf_len; i++) {
+        this_cp[i] = buf[i];
+      }
+      // Move string down to eliminate unneeded chars
+      memmove(this_cp + buf_len, this_cp + prev_cp_bytes, len - cp_idx);
+      // Null terminate the shorter string.
+      // Ensure string_len is not reduced because original 
+      // value still matters for GC purposes
+      raw[len - (prev_cp_bytes - buf_len)] = '\0'; 
+    }
+    // - 3) TODO: buf_len > prev_cp_bytes, will need to allocate more memory (!!)
+    else {
+      // TODO: maybe we can try a little harder here, at least in some cases
+      Cyc_rt_raise2(data, "string-set! - Unable to allocate memory to store multibyte character", chr);
+    }
+  }
   return str;
 }
 
@@ -2112,13 +2226,30 @@ object Cyc_string_ref(void *data, object str, object k)
 
   raw = string_str(str);
   idx = unbox_number(k);
-  len = string_len(str);
+  len = string_num_cp(str);
 
   if (idx < 0 || idx >= len) {
     Cyc_rt_raise2(data, "string-ref - invalid index", k);
   }
 
-  return obj_char2obj(raw[idx]);
+  // Take fast path if all chars are just 1 byte
+  if (string_num_cp(str) == string_len(str)) {
+    return obj_char2obj(raw[idx]);
+  } else {
+    char_type codepoint;
+    uint32_t state = 0;
+    int count;
+
+    for (count = 0; *raw; ++raw){
+      if (!Cyc_utf8_decode(&state, &codepoint, (uint8_t)*raw)){
+        if (count == idx) break; // Reached requested index
+        count += 1;
+      }
+    }
+    if (state != CYC_UTF8_ACCEPT)
+       Cyc_rt_raise2(data, "string-ref - invalid character at index", k);
+    return obj_char2obj(codepoint);
+  }
 }
 
 object Cyc_substring(void *data, object cont, object str, object start,
@@ -2134,7 +2265,7 @@ object Cyc_substring(void *data, object cont, object str, object start,
   raw = string_str(str);
   s = unbox_number(start);
   e = unbox_number(end);
-  len = string_len(str);
+  len = string_num_cp(str);
 
   if (s > e) {
     Cyc_rt_raise2(data, "substring - start cannot be greater than end", start);
@@ -2148,9 +2279,33 @@ object Cyc_substring(void *data, object cont, object str, object start,
     e = len;
   }
 
-  {
+  if (string_num_cp(str) == string_len(str)){ // Fast path for ASCII
     make_string_with_len(sub, raw + s, e - s);
     _return_closcall1(data, cont, &sub);
+  } else {
+    const char *tmp = raw;
+    char_type codepoint;
+    uint32_t state = 0;
+    int num_ch, cur_ch_bytes = 0, start_i = 0, end_i = 0;
+    for (num_ch = 0; *tmp; ++tmp){
+      cur_ch_bytes++;
+      if (!Cyc_utf8_decode(&state, &codepoint, (uint8_t)*tmp)){
+        end_i += cur_ch_bytes;
+        num_ch += 1;
+        cur_ch_bytes = 0;
+
+        if (num_ch == s) {
+          start_i = end_i;
+        }
+        if (num_ch == e) {
+          break;
+        }
+      }
+    }
+    if (state != CYC_UTF8_ACCEPT)
+       Cyc_rt_raise2(data, "substring - invalid character in string", str);
+    make_utf8_string_with_len(sub, raw + start_i, end_i - start_i, e - s);
+    _return_closcall1(data, cont, &sub);
   }
 }
 
@@ -2164,22 +2319,22 @@ object Cyc_installation_dir(void *data, object cont, object type)
       strncmp(((symbol) type)->desc, "sld", 5) == 0) {
     char buf[1024];
     snprintf(buf, sizeof(buf), "%s", CYC_INSTALL_SLD);
-    make_string(str, buf);
+    make_utf8_string(data, str, buf);
     _return_closcall1(data, cont, &str);
   } else if (Cyc_is_symbol(type) == boolean_t &&
              strncmp(((symbol) type)->desc, "lib", 5) == 0) {
     char buf[1024];
     snprintf(buf, sizeof(buf), "%s", CYC_INSTALL_LIB);
-    make_string(str, buf);
+    make_utf8_string(data, str, buf);
     _return_closcall1(data, cont, &str);
   } else if (Cyc_is_symbol(type) == boolean_t &&
              strncmp(((symbol) type)->desc, "inc", 5) == 0) {
     char buf[1024];
     snprintf(buf, sizeof(buf), "%s", CYC_INSTALL_INC);
-    make_string(str, buf);
+    make_utf8_string(data, str, buf);
     _return_closcall1(data, cont, &str);
   } else {
-    make_string(str, CYC_INSTALL_DIR);
+    make_utf8_string(data, str, CYC_INSTALL_DIR);
     _return_closcall1(data, cont, &str);
   }
 }
@@ -2193,22 +2348,22 @@ object Cyc_compilation_environment(void *data, object cont, object var)
     if (strncmp(((symbol) var)->desc, "cc-prog", 8) == 0) {
       char buf[1024];
       snprintf(buf, sizeof(buf), "%s", CYC_CC_PROG);
-      make_string(str, buf);
+      make_utf8_string(data, str, buf);
       _return_closcall1(data, cont, &str);
     } else if (strncmp(((symbol) var)->desc, "cc-exec", 8) == 0) {
       char buf[1024];
       snprintf(buf, sizeof(buf), "%s", CYC_CC_EXEC);
-      make_string(str, buf);
+      make_utf8_string(data, str, buf);
       _return_closcall1(data, cont, &str);
     } else if (strncmp(((symbol) var)->desc, "cc-lib", 7) == 0) {
       char buf[1024];
       snprintf(buf, sizeof(buf), "%s", CYC_CC_LIB);
-      make_string(str, buf);
+      make_utf8_string(data, str, buf);
       _return_closcall1(data, cont, &str);
     } else if (strncmp(((symbol) var)->desc, "cc-so", 6) == 0) {
       char buf[1024];
       snprintf(buf, sizeof(buf), "%s", CYC_CC_SO);
-      make_string(str, buf);
+      make_utf8_string(data, str, buf);
       _return_closcall1(data, cont, &str);
     }
   }
@@ -2234,7 +2389,7 @@ object Cyc_command_line_arguments(void *data, object cont)
   for (i = _cyc_argc; i > 1; i--) {     // skip program name
     object ps = alloca(sizeof(string_type));
     object pl = alloca(sizeof(pair_type));
-    make_string(s, _cyc_argv[i - 1]);
+    make_utf8_string(data, s, _cyc_argv[i - 1]);
     memcpy(ps, &s, sizeof(string_type));
     ((list) pl)->hdr.mark = gc_color_red;
     ((list) pl)->hdr.grayed = 0;
@@ -2490,6 +2645,10 @@ object Cyc_utf82string(void *data, object cont, object bv, object start,
     st.str = alloca(sizeof(char) * (len + 1));
     memcpy(st.str, &buf[s], len);
     st.str[len] = '\0';
+    st.num_cp = Cyc_utf8_count_code_points((uint8_t *)(st.str));
+    if (st.num_cp < 0) {
+       Cyc_rt_raise2(data, "utf8->string - error decoding UTF 8", bv);
+    }
     _return_closcall1(data, cont, &st);
   }
 }
@@ -2509,18 +2668,45 @@ object Cyc_string2utf8(void *data, object cont, object str, object start,
   e = unbox_number(end);
   len = e - s;
 
-  if (s < 0 || (s >= string_len(str) && len > 0)) {
+  if (s < 0 || (s >= string_num_cp(str) && len > 0)) {
     Cyc_rt_raise2(data, "string->utf8 - invalid start", start);
   }
 
-  if (e < 0 || e < s || e > string_len(str)) {
+  if (e < 0 || e < s || e > string_num_cp(str)) {
     Cyc_rt_raise2(data, "string->utf8 - invalid end", end);
   }
 
-  result.len = len;
-  result.data = alloca(sizeof(char) * len);
-  memcpy(&result.data[0], &(string_str(str))[s], len);
-  _return_closcall1(data, cont, &result);
+  // Fast path
+  if (string_num_cp(str) == string_len(str)) { // TODO: disable for testing purposes
+    result.len = len;
+    result.data = alloca(sizeof(char) * len);
+    memcpy(&result.data[0], &(string_str(str))[s], len);
+    _return_closcall1(data, cont, &result);
+  } else {
+    const char *tmp = string_str(str);
+    char_type codepoint;
+    uint32_t state = 0;
+    int num_ch, cur_ch_bytes = 0, start_i = 0, end_i = 0;
+    for (num_ch = 0; *tmp; ++tmp){
+      cur_ch_bytes++;
+      if (!Cyc_utf8_decode(&state, &codepoint, (uint8_t)*tmp)){
+        end_i += cur_ch_bytes;
+        num_ch += 1;
+        cur_ch_bytes = 0;
+
+        if (num_ch == s) {
+          start_i = end_i;
+        }
+        if (num_ch == e) {
+          break;
+        }
+      }
+    }
+    result.len = end_i - start_i;
+    result.data = alloca(sizeof(char) * result.len);
+    memcpy(&result.data[0], &(string_str(str))[start_i], result.len);
+    _return_closcall1(data, cont, &result);
+  }
 }
 
 object Cyc_bytevector_u8_ref(void *data, object bv, object k)
@@ -2624,7 +2810,7 @@ object Cyc_char2integer(object chr)
 
 object Cyc_integer2char(void *data, object n)
 {
-  int val = 0;
+  char_type val = 0;
 
   Cyc_check_num(data, n);
   val = unbox_number(n);
@@ -5635,7 +5821,7 @@ void Cyc_import_shared_object(void *data, object cont, object filename, object e
   handle = dlopen(string_str(filename), RTLD_GLOBAL | RTLD_LAZY);
   if (handle == NULL) {
     snprintf(buffer, 256, "%s", dlerror());
-    make_string(s, buffer);
+    make_utf8_string(data, s, buffer);
     Cyc_rt_raise2(data, "Unable to import library", &s);
   }
   dlerror();    /* Clear any existing error */
@@ -5643,7 +5829,7 @@ void Cyc_import_shared_object(void *data, object cont, object filename, object e
   entry_pt = (function_type) dlsym(handle, string_str(entry_pt_fnc));
   if (entry_pt == NULL) {
     snprintf(buffer, 256, "%s, %s, %s", string_str(filename), string_str(entry_pt_fnc), dlerror());
-    make_string(s, buffer);
+    make_utf8_string(data, s, buffer);
     Cyc_rt_raise2(data, "Unable to load symbol", &s);
   }
   mclosure1(clo, entry_pt, cont);
@@ -5692,6 +5878,7 @@ void _read_error(void *data, port_type *p, const char *msg)
   // the cont could receive an error and raise it though
   //Cyc_rt_raise_msg(data, buf);
   make_string(str, buf);
+  str.num_cp = Cyc_utf8_count_code_points((uint8_t *)buf);
   make_empty_vector(vec);
   vec.num_elements = 1;
   vec.elements = (object *) alloca(sizeof(object) * vec.num_elements);
@@ -5804,6 +5991,28 @@ static void _read_add_to_tok_buf(port_type *p, char c)
   p->tok_buf[p->tok_end++] = c;
 }
 
+/**
+ * @brief Determine if given string is numeric
+ */
+int _read_is_numeric(const char *tok)
+{
+  int len = strlen(tok);
+  return (len &&
+          ((isdigit(tok[0])) ||
+           ((len > 1) && tok[0] == '.' && isdigit(tok[1])) ||
+           ((len > 1) && (tok[1] == '.' || isdigit(tok[1])) && (tok[0] == '-' || tok[0] == '+'))));
+}
+
+/**
+ * @brief Helper function, determine if given number is a hex digit
+ * @param c Character to check
+ */
+int _read_is_hex_digit(char c)
+{
+  return (c >= 'a' && c <= 'f') ||
+         (c >= 'A' && c <= 'F');
+}
+
 /**
  * @brief Helper function to read a string
  * @param data Thread data object
@@ -5863,6 +6072,12 @@ void _read_string(void *data, object cont, port_type *p)
             p->buf_idx++;
             break;
           }
+          // Verify if hex digit is valid
+          if (!isdigit(p->mem_buf[p->buf_idx]) && 
+              !_read_is_hex_digit(p->mem_buf[p->buf_idx])) {
+            p->buf_idx++;
+            _read_error(data, p, "invalid hex digit in string");
+          }
           buf[i] = p->mem_buf[p->buf_idx];
           p->buf_idx++;
           p->col_num++;
@@ -5870,8 +6085,14 @@ void _read_string(void *data, object cont, port_type *p)
         }
         buf[i] = '\0';
         {
-          int result = (int)strtol(buf, NULL, 16);
-          p->tok_buf[p->tok_end++] = (char)result;
+          char_type result = strtol(buf, NULL, 16);
+          char cbuf[5];
+          int i;
+          Cyc_utf8_encode_char(cbuf, 5, result);
+          for (i = 0; cbuf[i] != 0; i++) {
+            _read_add_to_tok_buf(p, cbuf[i]);
+          }
+          //p->tok_buf[p->tok_end++] = (char)result;
         }
         break;
       }
@@ -5883,7 +6104,7 @@ void _read_string(void *data, object cont, port_type *p)
       p->tok_buf[p->tok_end] = '\0'; // TODO: what if buffer is full?
       p->tok_end = 0; // Reset for next atom
       {
-        make_string(str, p->tok_buf);
+        make_utf8_string(data, str, p->tok_buf);
         return_thread_runnable(data, &str);
       }
     } else if (c == '\\') {
@@ -5943,6 +6164,7 @@ void _read_return_character(void *data, port_type *p)
   p->tok_buf[p->tok_end] = '\0'; // TODO: what if buffer is full?
   p->tok_end = 0; // Reset for next atom
   if (strlen(p->tok_buf) == 1) {
+    // ASCII char, consider merging with below?
     return_thread_runnable(data, obj_char2obj(p->tok_buf[0]));
   } else if(strncmp(p->tok_buf, "alarm", 5) == 0) {
     return_thread_runnable(data, obj_char2obj('\a'));
@@ -5964,12 +6186,27 @@ void _read_return_character(void *data, port_type *p)
     return_thread_runnable(data, obj_char2obj('\t'));
   } else if(strlen(p->tok_buf) > 1 && p->tok_buf[0] == 'x') {
     const char *buf = p->tok_buf + 1;
-    int result = strtol(buf, NULL, 16);
+    char_type result = strtol(buf, NULL, 16);
     return_thread_runnable(data, obj_char2obj(result));
   } else {
-    char buf[31];
-    snprintf(buf, 30, "Unable to parse character %s", p->tok_buf);
-    _read_error(data, p, buf);
+    // Try to read a UTF-8 char and if so return it, otherwise throw an error
+    uint32_t state = CYC_UTF8_ACCEPT;
+    char_type codepoint;
+    uint8_t *s = (uint8_t *)p->tok_buf;
+    while(s) {
+      if (!Cyc_utf8_decode(&state, &codepoint, *s)) {
+        s++;
+        break;
+      }
+      s++;
+    }
+    if (state == CYC_UTF8_ACCEPT && *s == '\0') {
+      return_thread_runnable(data, obj_char2obj(codepoint));
+    } else {
+      char buf[31];
+      snprintf(buf, 30, "Unable to parse character %s", p->tok_buf);
+      _read_error(data, p, buf);
+    }
   }
 }
 
@@ -6001,28 +6238,6 @@ void _read_character(void *data, port_type *p)
   }
 }
 
-/**
- * @brief Determine if given string is numeric
- */
-int _read_is_numeric(const char *tok)
-{
-  int len = strlen(tok);
-  return (len &&
-          ((isdigit(tok[0])) ||
-           ((len > 1) && tok[0] == '.' && isdigit(tok[1])) ||
-           ((len > 1) && (tok[1] == '.' || isdigit(tok[1])) && (tok[0] == '-' || tok[0] == '+'))));
-}
-
-/**
- * @brief Helper function, determine if given number is a hex digit
- * @param c Character to check
- */
-int _read_is_hex_digit(char c)
-{
-  return (c >= 'a' && c <= 'f') ||
-         (c >= 'A' && c <= 'F');
-}
-
 /**
  * @brief Helper function, return read number.
  * @param data Thread data object
@@ -6102,6 +6317,7 @@ void _read_return_atom(void *data, object cont, port_type *p)
 
   if (_read_is_numeric(p->tok_buf)) {
     make_string(str, p->tok_buf);
+    str.num_cp = Cyc_utf8_count_code_points((uint8_t *)(p->tok_buf));
     make_c_opaque(opq, &str);
     return_thread_runnable(data, &opq);
   } else if (strncmp("+inf.0", p->tok_buf, 6) == 0 ||
@@ -6134,7 +6350,10 @@ object Cyc_io_peek_char(void *data, object cont, object port)
 {
   FILE *stream;
   port_type *p;
-  int c;
+  uint32_t state = CYC_UTF8_ACCEPT;
+  char_type codepoint;
+  int c, i = 0, at_mem_buf_end = 0;
+  char buf[5];
 
   Cyc_check_port(data, port);
   {
@@ -6144,9 +6363,40 @@ object Cyc_io_peek_char(void *data, object cont, object port)
       Cyc_rt_raise2(data, "Unable to read from closed port: ", port);
     }
     set_thread_blocked(data, cont);
-    _read_next_char(data, cont, p);
+    if (p->mem_buf_len == 0 || p->mem_buf_len == p->buf_idx) {
+      _read_next_char(data, cont, p);
+    }
     c = p->mem_buf[p->buf_idx];
-    return_thread_runnable(data, (c != EOF) ? obj_char2obj(c) : Cyc_EOF);
+    if (Cyc_utf8_decode(&state, &codepoint, (uint8_t)c)) {
+      // Only have a partial UTF8 code point, read more chars.
+      // Problem is that there may not be enough space to store them
+      // and do need to set them aside since we are just peeking here
+      // and not actually supposed to be reading past chars.
+
+      buf[0] = c;
+      i = 1;
+      while (i < 5) { // TODO: limit to 4 chars??
+        if (p->mem_buf_len == p->buf_idx + i) {
+          // No more buffered chars
+          at_mem_buf_end = 1;
+          c = fgetc(stream);
+          if (c == EOF) break; // TODO: correct to do this here????
+        } else {
+          c = p->mem_buf[p->buf_idx + i];
+        }
+        buf[i++] = c;
+        if (!Cyc_utf8_decode(&state, &codepoint, (uint8_t)c)) {
+          break;
+        }
+      }
+    }
+    if (at_mem_buf_end && c != EOF) {
+      p->buf_idx = 0;
+      p->mem_buf_len = i;
+      memmove(p->mem_buf, buf, i);
+    }
+
+    return_thread_runnable(data, (c != EOF) ? obj_char2obj(codepoint) : Cyc_EOF);
   }
   return Cyc_EOF;
 }
@@ -6171,17 +6421,23 @@ object Cyc_io_peek_char(void *data, object cont, object port)
 object Cyc_io_read_char(void *data, object cont, object port)
 {
   port_type *p = (port_type *)port;
-  int c;
   Cyc_check_port(data, port);
   if (p->fp == NULL) {
     Cyc_rt_raise2(data, "Unable to read from closed port: ", port);
   }
   {
+    uint32_t state = CYC_UTF8_ACCEPT;
+    char_type codepoint;
+    int c;
     set_thread_blocked(data, cont);
-    _read_next_char(data, cont, p);
-    c = p->mem_buf[p->buf_idx++];
+    do {
+      _read_next_char(data, cont, p);
+      c = p->mem_buf[p->buf_idx++];
+      if (c == EOF) break;
+    } while(Cyc_utf8_decode(&state, &codepoint, (uint8_t)c));
+// TODO: limit above to 4 chars and then thrown an error?
     p->col_num++;
-    return_thread_runnable(data, (c != EOF) ? obj_char2obj(c) : Cyc_EOF);
+    return_thread_runnable(data, (c != EOF) ? obj_char2obj(codepoint) : Cyc_EOF);
   }
   return Cyc_EOF;
 }
@@ -6190,8 +6446,10 @@ object Cyc_io_read_char(void *data, object cont, object port)
 object Cyc_io_read_line(void *data, object cont, object port)
 {
   FILE *stream = ((port_type *) port)->fp;
-  char buf[1024];
-  int len;
+  char buf[1027];
+  int len, num_cp, i = 0;
+  char_type codepoint;
+  uint32_t state;
 
   Cyc_check_port(data, port);
   if (stream == NULL) {
@@ -6200,7 +6458,21 @@ object Cyc_io_read_line(void *data, object cont, object port)
   set_thread_blocked(data, cont);
   errno = 0;
   if (fgets(buf, 1023, stream) != NULL) {
-    len = strlen(buf);
+    state = Cyc_utf8_count_code_points_and_bytes((uint8_t *)buf, &codepoint, &num_cp, &len);
+    // Check if we stopped reading in the middle of a code point and
+    // if so, read one byte at a time until that code point is finished.
+    while (state != CYC_UTF8_ACCEPT && i < 3) {
+      int c = fgetc(stream);
+      buf[len] = c;
+      len++;
+      Cyc_utf8_decode(&state, &codepoint, (uint8_t)c);
+      if (state == CYC_UTF8_ACCEPT) {
+        num_cp++;
+        break;
+      }
+      i++;
+    }
+
     {
       // Remove any trailing CR / newline chars
       while (len > 0 && (buf[len - 1] == '\n' ||
@@ -6209,6 +6481,7 @@ object Cyc_io_read_line(void *data, object cont, object port)
       }
       buf[len] = '\0';
       make_string_noalloc(s, buf, len);
+      s.num_cp = num_cp;
       return_thread_runnable(data, &s);
     }
   } else {
@@ -6364,3 +6637,189 @@ void Cyc_io_read_token(void *data, object cont, object port)
   }
 }
 
+////////////// UTF-8 Section //////////////
+
+// Copyright (c) 2008-2009 Bjoern Hoehrmann <bjoern@hoehrmann.de>
+// See http://bjoern.hoehrmann.de/utf-8/decoder/dfa/ for details.
+static const uint8_t utf8d[] = {
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 00..1f
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 20..3f
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 40..5f
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 60..7f
+  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9, // 80..9f
+  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7, // a0..bf
+  8,8,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, // c0..df
+  0xa,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x4,0x3,0x3, // e0..ef
+  0xb,0x6,0x6,0x6,0x5,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8, // f0..ff
+  0x0,0x1,0x2,0x3,0x5,0x8,0x7,0x1,0x1,0x1,0x4,0x6,0x1,0x1,0x1,0x1, // s0..s0
+  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,1,1,1,1,0,1,0,1,1,1,1,1,1, // s1..s2
+  1,2,1,1,1,1,1,2,1,2,1,1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,1,1,1,1,1,1, // s3..s4
+  1,2,1,1,1,1,1,1,1,2,1,1,1,1,1,1,1,1,1,1,1,1,1,3,1,3,1,1,1,1,1,1, // s5..s6
+  1,3,1,1,1,1,1,3,1,3,1,1,1,1,1,1,1,3,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // s7..s8
+};
+
+//uint32_t inline
+uint32_t Cyc_utf8_decode(uint32_t* state, uint32_t* codep, uint32_t byte) {
+  uint32_t type = utf8d[byte];
+
+  *codep = (*state != CYC_UTF8_ACCEPT) ?
+    (byte & 0x3fu) | (*codep << 6) :
+    (0xff >> type) & (byte);
+
+  *state = utf8d[256 + *state*16 + type];
+  return *state;
+}
+// END Bjoern Hoehrmann
+
+/**
+ * @brief
+ * Count the number of code points in a string.
+ * Based on example code from Bjoern Hoehrmann.
+ */
+int Cyc_utf8_count_code_points(uint8_t* s) {
+  uint32_t codepoint;
+  uint32_t state = 0;
+  int count;
+
+  for (count = 0; *s; ++s)
+    if (!Cyc_utf8_decode(&state, &codepoint, *s))
+      count += 1;
+
+  if (state != CYC_UTF8_ACCEPT)
+    return -1;
+  return count;
+}
+
+int Cyc_utf8_count_code_points_and_bytes(uint8_t* s, char_type *codepoint, int *cpts, int *bytes) {
+  uint32_t state = 0;
+  *cpts = 0;
+  *bytes = 0;
+  for (; *s; ++s){
+    *bytes += 1;
+    if (!Cyc_utf8_decode(&state, codepoint, *s))
+      *cpts += 1;
+  }
+
+  if (state != CYC_UTF8_ACCEPT)
+    return state;
+  return 0;
+}
+
+// TODO: index into X codepoint in a string 
+
+/**
+ * @brief
+ * Use this when validating from a stream, as it may be that the stream stopped
+ * in the middle of a codepoint, hence state passed in as an arg, so it can be
+ * tested in a loop and also after the loop has finished.
+ *
+ * From https://stackoverflow.com/a/22135005/101258
+ */
+uint32_t Cyc_utf8_validate_stream(uint32_t *state, char *str, size_t len) {
+   size_t i;
+   uint32_t type;
+
+    for (i = 0; i < len; i++) {
+        // We don't care about the codepoint, so this is
+        // a simplified version of the decode function.
+        type = utf8d[(uint8_t)str[i]];
+        *state = utf8d[256 + (*state) * 16 + type];
+
+        if (*state == CYC_UTF8_REJECT)
+            break;
+    }
+
+    return *state;
+}
+
+/**
+ * @brief Simplified version of Cyc_utf8_validate_stream that must always be called with a complete string buffer.
+ */
+uint32_t Cyc_utf8_validate(char *str, size_t len) {
+   size_t i;
+   uint32_t state = CYC_UTF8_ACCEPT, type;
+
+    for (i = 0; i < len; i++) {
+        // We don't care about the codepoint, so this is
+        // a simplified version of the decode function.
+        type = utf8d[(uint8_t)str[i]];
+        state = utf8d[256 + (state) * 16 + type];
+
+        if (state == CYC_UTF8_REJECT)
+            break;
+    }
+
+    return state;
+}
+
+//int uint32_num_bytes(uint32_t x) {
+//  // TODO: could compute log(val) / log(256)
+//  if (x < 0x100) return 1;
+//  if (x < 0x10000) return 2;
+//  if (x < 0x1000000) return 3;
+//  return 4;
+//}
+
+/**
+ * This function takes one or more 32-bit chars and encodes them 
+ * as an array of UTF-8 bytes.
+ * FROM: https://www.cprogramming.com/tutorial/utf8.c
+ *
+ * @param dest    Destination byte buffer
+ * @param sz      size of dest buffer in bytes
+ * @param src     Buffer of source data, in 32-bit characters
+ * @param srcsz   number of source characters, or -1 if 0-terminated
+ *
+ * @return Number of characters converted
+ *
+ * dest will only be '\0'-terminated if there is enough space. this is
+ * for consistency; imagine there are 2 bytes of space left, but the next
+ * character requires 3 bytes. in this case we could NUL-terminate, but in
+ * general we can't when there's insufficient space. therefore this function
+ * only NUL-terminates if all the characters fit, and there's space for
+ * the NUL as well.
+ * the destination string will never be bigger than the source string.
+ */
+int Cyc_utf8_encode(char *dest, int sz, uint32_t *src, int srcsz)
+{
+    u_int32_t ch;
+    int i = 0;
+    char *dest_end = dest + sz;
+
+    while (srcsz<0 ? src[i]!=0 : i < srcsz) {
+        ch = src[i];
+        if (ch < 0x80) {
+            if (dest >= dest_end)
+                return i;
+            *dest++ = (char)ch;
+        }
+        else if (ch < 0x800) {
+            if (dest >= dest_end-1)
+                return i;
+            *dest++ = (ch>>6) | 0xC0;
+            *dest++ = (ch & 0x3F) | 0x80;
+        }
+        else if (ch < 0x10000) {
+            if (dest >= dest_end-2)
+                return i;
+            *dest++ = (ch>>12) | 0xE0;
+            *dest++ = ((ch>>6) & 0x3F) | 0x80;
+            *dest++ = (ch & 0x3F) | 0x80;
+        }
+        else if (ch < 0x110000) {
+            if (dest >= dest_end-3)
+                return i;
+            *dest++ = (ch>>18) | 0xF0;
+            *dest++ = ((ch>>12) & 0x3F) | 0x80;
+            *dest++ = ((ch>>6) & 0x3F) | 0x80;
+            *dest++ = (ch & 0x3F) | 0x80;
+        }
+        i++;
+    }
+    if (dest < dest_end)
+        *dest = '\0';
+    return i;
+}
+
+
+////////////// END UTF-8 Section //////////////
diff --git a/scheme/base.sld b/scheme/base.sld
index 75ecc2f1..c13cde79 100644
--- a/scheme/base.sld
+++ b/scheme/base.sld
@@ -950,9 +950,22 @@
     (define-c Cyc-make-string
       "(void *data, int argc, closure _, object k, object count, object fill)"
       " object s = NULL;
+        char ch_buf[5];
+        char_type c;
+        int buflen, num_cp, len;
         Cyc_check_int(data, count);
-        char c = obj_obj2char(fill);
-        int len = obj_obj2int(count);
+        if (!obj_is_char(fill)) {
+          Cyc_rt_raise2(data, \"Expected character buf received\", fill);
+        }
+        c = obj_obj2char(fill);
+        if (!c) {
+          buflen = 1;
+        } else {
+          Cyc_utf8_encode_char(ch_buf, 5, c);
+          buflen = strlen(ch_buf);
+        }
+        num_cp = obj_obj2int(count);
+        len = num_cp * buflen;
         if (len >= MAX_STACK_OBJ) {
           int heap_grown;
           s = gc_alloc(((gc_thread_data *)data)->heap, 
@@ -964,6 +977,7 @@
           ((string_type *) s)->hdr.grayed = 0;
           ((string_type *) s)->tag = string_tag; 
           ((string_type *) s)->len = len;
+          ((string_type *) s)->num_cp = num_cp;
           ((string_type *) s)->str = (((char *)s) + sizeof(string_type));
         } else {
           s = alloca(sizeof(string_type));
@@ -971,9 +985,18 @@
           ((string_type *)s)->hdr.grayed = 0;
           ((string_type *)s)->tag = string_tag; 
           ((string_type *)s)->len = len;
+          ((string_type *)s)->num_cp = num_cp;
           ((string_type *)s)->str = alloca(sizeof(char) * (len + 1));
         }
-        memset(((string_type *)s)->str, c, len);
+        if (num_cp == 1) { /* Fast path */
+          memset(((string_type *)s)->str, ch_buf[0], len);
+        } else {
+          char *buf = ((string_type *)s)->str;
+          int bi, si, slen = buflen;
+          for (bi = 0, si = 0; bi < len; bi++, si++) {
+            buf[bi] = ch_buf[si % slen];
+          }
+        }
         ((string_type *)s)->str[len] = '\\0';
         return_closcall1(data, k, s);
       ")
diff --git a/scheme/cyclone/cgen.sld b/scheme/cyclone/cgen.sld
index 7cdd74f0..d3456d11 100644
--- a/scheme/cyclone/cgen.sld
+++ b/scheme/cyclone/cgen.sld
@@ -521,7 +521,15 @@
             (string-append "&" cvar-name) ; Code is just the variable name
             (list     ; Allocate integer on the C stack
               (string-append 
-                "make_string(" cvar-name ", " (->cstr exp) ");")))))
+                "make_utf8_string_with_len(" 
+                cvar-name 
+                ", " 
+                (->cstr exp) 
+                ", " 
+                (number->string (string-byte-length exp))
+                ", " 
+                (number->string (string-length exp))
+                ");")))))
 ;TODO: not good enough, need to store new symbols in a table so they can
 ;be inserted into the C program
     ((symbol? exp)
@@ -536,6 +544,10 @@
 (define (->cstr str) 
   (string-append "\"" (cstr:escape-chars str) "\""))
 
+(define-c string-byte-length
+  "(void *data, int argc, closure _, object k, object s)"
+  " return_closcall1(data, k, Cyc_string_byte_length(data, s)); ")
+
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ;; Primitives
 
diff --git a/scheme/process-context.sld b/scheme/process-context.sld
index f8ce64f2..e5cfa5c3 100644
--- a/scheme/process-context.sld
+++ b/scheme/process-context.sld
@@ -24,7 +24,7 @@
         for (i = _cyc_argc; i > 0; i--) {
           object ps = alloca(sizeof(string_type));
           object pl = alloca(sizeof(pair_type));
-          make_string(s, _cyc_argv[i - 1]);
+          make_utf8_string(data, s, _cyc_argv[i - 1]);
           memcpy(ps, &s, sizeof(string_type));
           ((list)pl)->hdr.mark = gc_color_red;
           ((list)pl)->hdr.grayed = 0;
@@ -44,7 +44,7 @@
         if (v == NULL) {
           return_closcall1(data, k, boolean_f);
         } else {
-          make_string(str, v);
+          make_utf8_string(data, str, v);
           return_closcall1(data, k, &str);
         }
       ")
diff --git a/test.c b/test.c
new file mode 100644
index 00000000..434c33cd
--- /dev/null
+++ b/test.c
@@ -0,0 +1,193 @@
+// A temporary test file
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdint.h>
+#include <string.h>
+
+#define CYC_UTF8_ACCEPT 0
+
+// Copyright (c) 2008-2009 Bjoern Hoehrmann <bjoern@hoehrmann.de>
+// See http://bjoern.hoehrmann.de/utf-8/decoder/dfa/ for details.
+static const uint8_t utf8d[] = {
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 00..1f
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 20..3f
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 40..5f
+  0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0, // 60..7f
+  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9, // 80..9f
+  7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7, // a0..bf
+  8,8,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2,2, // c0..df
+  0xa,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x3,0x4,0x3,0x3, // e0..ef
+  0xb,0x6,0x6,0x6,0x5,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8,0x8, // f0..ff
+  0x0,0x1,0x2,0x3,0x5,0x8,0x7,0x1,0x1,0x1,0x4,0x6,0x1,0x1,0x1,0x1, // s0..s0
+  1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,1,1,1,1,1,0,1,0,1,1,1,1,1,1, // s1..s2
+  1,2,1,1,1,1,1,2,1,2,1,1,1,1,1,1,1,1,1,1,1,1,1,2,1,1,1,1,1,1,1,1, // s3..s4
+  1,2,1,1,1,1,1,1,1,2,1,1,1,1,1,1,1,1,1,1,1,1,1,3,1,3,1,1,1,1,1,1, // s5..s6
+  1,3,1,1,1,1,1,3,1,3,1,1,1,1,1,1,1,3,1,1,1,1,1,1,1,1,1,1,1,1,1,1, // s7..s8
+};
+
+//uint32_t inline
+uint32_t Cyc_utf8_decode(uint32_t* state, uint32_t* codep, uint32_t byte) {
+  uint32_t type = utf8d[byte];
+
+  *codep = (*state != CYC_UTF8_ACCEPT) ?
+    (byte & 0x3fu) | (*codep << 6) :
+    (0xff >> type) & (byte);
+
+  *state = utf8d[256 + *state*16 + type];
+  return *state;
+}
+
+/**
+ * Simple macro to make it more convenient to convert a single char
+ */
+#define Cyc_utf8_encode_char(dest, dest_size, char_value) \
+  Cyc_utf8_encode(dest, dest_size, &char_value, 1)
+
+/**
+ * This function takes one or more 32-bit chars and encodes them 
+ * as an array of UTF-8 bytes.
+ * FROM: https://www.cprogramming.com/tutorial/utf8.c
+ *
+ * @param dest    Destination byte buffer
+ * @param sz      size of dest buffer in bytes
+ * @param src     Buffer of source data, in 32-bit characters
+ * @param srcsz   number of source characters, or -1 if 0-terminated
+ *
+ * @return Number of characters converted
+ *
+ * dest will only be '\0'-terminated if there is enough space. this is
+ * for consistency; imagine there are 2 bytes of space left, but the next
+ * character requires 3 bytes. in this case we could NUL-terminate, but in
+ * general we can't when there's insufficient space. therefore this function
+ * only NUL-terminates if all the characters fit, and there's space for
+ * the NUL as well.
+ * the destination string will never be bigger than the source string.
+ */
+int Cyc_utf8_encode(char *dest, int sz, uint32_t *src, int srcsz)
+{
+    u_int32_t ch;
+    int i = 0;
+    char *dest_end = dest + sz;
+
+    while (srcsz<0 ? src[i]!=0 : i < srcsz) {
+        ch = src[i];
+        if (ch < 0x80) {
+            if (dest >= dest_end)
+                return i;
+            *dest++ = (char)ch;
+        }
+        else if (ch < 0x800) {
+            if (dest >= dest_end-1)
+                return i;
+            *dest++ = (ch>>6) | 0xC0;
+            *dest++ = (ch & 0x3F) | 0x80;
+        }
+        else if (ch < 0x10000) {
+            if (dest >= dest_end-2)
+                return i;
+            *dest++ = (ch>>12) | 0xE0;
+            *dest++ = ((ch>>6) & 0x3F) | 0x80;
+            *dest++ = (ch & 0x3F) | 0x80;
+        }
+        else if (ch < 0x110000) {
+            if (dest >= dest_end-3)
+                return i;
+            *dest++ = (ch>>18) | 0xF0;
+            *dest++ = ((ch>>12) & 0x3F) | 0x80;
+            *dest++ = ((ch>>6) & 0x3F) | 0x80;
+            *dest++ = (ch & 0x3F) | 0x80;
+        }
+        i++;
+    }
+    if (dest < dest_end)
+        *dest = '\0';
+    return i;
+}
+
+void encode(uint32_t val) {
+  char dest[5];
+  int rv, i;
+
+  rv = Cyc_utf8_encode_char(dest, 5, val);
+  printf("%x %d \n", val, rv);
+  for(i = 0; i < 5; i++) {
+    printf("[%x] ", (uint8_t)dest[i]);
+  }
+  printf("\n");
+  return;
+}
+
+void multi_byte_memset(char *buf, int blen, char *src, int slen)
+{
+  int bi, si;
+  for (bi = 0, si = 0; bi < blen; bi++, si++) {
+    buf[bi] = src[si % slen];
+  }
+}
+
+void substring(int s, int e, const char *expected) {
+  uint8_t raw[] = {65, 66, 0xCE, 0xBB, 67};
+    const char *tmp = raw;
+    uint32_t codepoint;
+    uint32_t state = 0;
+    int num_ch, cur_ch_bytes = 0, start_i = 0, end_i = 0;
+    for (num_ch = 0; *tmp; ++tmp){
+      cur_ch_bytes++;
+      if (!Cyc_utf8_decode(&state, &codepoint, (uint8_t)*tmp)){
+        end_i += cur_ch_bytes;
+        num_ch += 1;
+        cur_ch_bytes = 0;
+
+        if (num_ch == s) {
+          start_i = end_i;
+        }
+        if (num_ch == e) {
+          break;
+        }
+      }
+    }
+    raw[end_i] = '\0';
+    printf("expected=%s, raw=%s, s=%d, e=%d, start_i=%d, end_i=%d\n", expected, raw + start_i, s, e, start_i, end_i);
+}
+
+void main(){
+  char c[128];
+  uint8_t cv[] = {0xEC, 0xBA, 0xBB, 0x00}; // Lambda (0x03bb) is encoded with leading 0xCE
+  uint8_t cv2[] = {0xCE, 0xBB}; // Lambda (0x03bb) is encoded with leading 0xCE
+  //uint8_t cv2[] = {0xEC, 0xBA, 0xBB}; // Lambda (0x03bb) is encoded with leading 0xCE
+//  uint8_t cv[] = {0xCE, 0xBB, 0x00}; // Lambda (0x03bb) is encoded with leading 0xCE
+  char *cptr;
+  uint32_t state = CYC_UTF8_ACCEPT, codepoint, val = 0x32363435;
+  uint8_t *ptr = (uint8_t *)&val;
+  int i, j = 0;
+//  //memset(c, 0x34, 128);
+//  for (i = 0; i < 127; i++) {
+//    c[i] = ptr[j++];    
+//    if (j == 4) j = 0;
+//  }
+//  c[127] = '\0';
+//  printf("%s\n", c);
+  multi_byte_memset(c, 126, cv2, 2);
+  c[127] = '\0';
+  printf("TEST: %s\n", c);
+
+  ptr = cv;
+  for (i = 0; i < 3; i++) {
+    Cyc_utf8_decode(&state, &codepoint, ptr[i]);
+  }
+  printf("state = %d, cp = %d\n", state, codepoint);
+
+  encode(0x3bb);
+  encode(65);
+  encode(0xcebb);
+
+  printf("%06X\n", 0x0fff);
+  substring(0, 1, "A   ");
+  substring(0, 2, "AB  ");
+  substring(1, 3, "Bx  ");
+  substring(1, 4, "BxC ");
+  substring(2, 2, "    ");
+  substring(2, 3, "x   ");
+  substring(2, 4, "xC  ");
+  return;
+}