diff --git a/src/primitives.c b/src/primitives.c
index ca1b0ba4..594b0c43 100644
--- a/src/primitives.c
+++ b/src/primitives.c
@@ -23,42 +23,54 @@
 
 DEF_PRIMITIVE(num_abs)
 {
-  double value = ((ObjNum*)args[0])->value;
+  double value = AS_NUM(args[0]);
   if (value < 0) value = -value;
 
   return (Value)makeNum(value);
 }
 
+DEF_PRIMITIVE(num_toString)
+{
+  // TODO(bob): What size should this be?
+  char temp[100];
+  sprintf(temp, "%g", AS_NUM(args[0]));
+
+  size_t size = strlen(temp) + 1;
+  char* result = malloc(size);
+  strncpy(result, temp, size);
+  return (Value)makeString(result);
+}
+
 DEF_PRIMITIVE(num_minus)
 {
   if (args[1]->type != OBJ_NUM) return vm->unsupported;
-  return (Value)makeNum(((ObjNum*)args[0])->value - ((ObjNum*)args[1])->value);
+  return (Value)makeNum(AS_NUM(args[0]) - AS_NUM(args[1]));
 }
 
 DEF_PRIMITIVE(num_plus)
 {
   if (args[1]->type != OBJ_NUM) return vm->unsupported;
   // TODO(bob): Handle coercion to string if RHS is a string.
-  return (Value)makeNum(((ObjNum*)args[0])->value + ((ObjNum*)args[1])->value);
+  return (Value)makeNum(AS_NUM(args[0]) + AS_NUM(args[1]));
 }
 
 DEF_PRIMITIVE(num_multiply)
 {
   if (args[1]->type != OBJ_NUM) return vm->unsupported;
-  return (Value)makeNum(((ObjNum*)args[0])->value * ((ObjNum*)args[1])->value);
+  return (Value)makeNum(AS_NUM(args[0]) * AS_NUM(args[1]));
 }
 
 DEF_PRIMITIVE(num_divide)
 {
   if (args[1]->type != OBJ_NUM) return vm->unsupported;
-  return (Value)makeNum(((ObjNum*)args[0])->value / ((ObjNum*)args[1])->value);
+  return (Value)makeNum(AS_NUM(args[0]) / AS_NUM(args[1]));
 }
 
 DEF_PRIMITIVE(string_contains)
 {
-  const char* string = ((ObjString*)args[0])->value;
+  const char* string = AS_STRING(args[0]);
   // TODO(bob): Check type of arg first!
-  const char* search = ((ObjString*)args[1])->value;
+  const char* search = AS_STRING(args[1]);
 
   // Corner case, the empty string contains the empty string.
   if (strlen(string) == 0 && strlen(search) == 0) return (Value)makeNum(1);
@@ -69,25 +81,29 @@ DEF_PRIMITIVE(string_contains)
 
 DEF_PRIMITIVE(string_count)
 {
-  double count = strlen(((ObjString*)args[0])->value);
-
+  double count = strlen(AS_STRING(args[0]));
   return (Value)makeNum(count);
 }
 
+DEF_PRIMITIVE(string_toString)
+{
+  return args[0];
+}
+
 DEF_PRIMITIVE(string_plus)
 {
   if (args[1]->type != OBJ_STRING) return vm->unsupported;
   // TODO(bob): Handle coercion to string of RHS.
 
-  ObjString* left = (ObjString*)args[0];
-  ObjString* right = (ObjString*)args[1];
+  const char* left = AS_STRING(args[0]);
+  const char* right = AS_STRING(args[1]);
 
-  size_t leftLength = strlen(left->value);
-  size_t rightLength = strlen(right->value);
+  size_t leftLength = strlen(left);
+  size_t rightLength = strlen(right);
 
   char* result = malloc(leftLength + rightLength);
-  strcpy(result, left->value);
-  strcpy(result + leftLength, right->value);
+  strcpy(result, left);
+  strcpy(result + leftLength, right);
   
   return (Value)makeString(result);
 }
@@ -102,6 +118,7 @@ DEF_PRIMITIVE(io_write)
 void registerPrimitives(VM* vm)
 {
   PRIMITIVE(vm->numClass, "abs", num_abs);
+  PRIMITIVE(vm->numClass, "toString", num_toString)
   PRIMITIVE(vm->numClass, "- ", num_minus);
   PRIMITIVE(vm->numClass, "+ ", num_plus);
   PRIMITIVE(vm->numClass, "* ", num_multiply);
@@ -109,6 +126,7 @@ void registerPrimitives(VM* vm)
 
   PRIMITIVE(vm->stringClass, "contains ", string_contains);
   PRIMITIVE(vm->stringClass, "count", string_count);
+  PRIMITIVE(vm->stringClass, "toString", string_toString)
   PRIMITIVE(vm->stringClass, "+ ", string_plus);
 
   ObjClass* ioClass = makeClass();
diff --git a/src/vm.h b/src/vm.h
index 727b49ec..448c2924 100644
--- a/src/vm.h
+++ b/src/vm.h
@@ -6,6 +6,12 @@
 #define MAX_CALL_FRAMES 256
 #define MAX_SYMBOLS 256
 
+// Get the double value of [obj], which must be a number.
+#define AS_NUM(obj) (((ObjNum*)obj)->value)
+
+// Get the const char* value of [obj], which must be a string.
+#define AS_STRING(obj) (((ObjString*)obj)->value)
+
 typedef enum {
   OBJ_BLOCK,
   OBJ_CLASS,
diff --git a/test/number_to_string.wren b/test/number_to_string.wren
new file mode 100644
index 00000000..57453776
--- /dev/null
+++ b/test/number_to_string.wren
@@ -0,0 +1,7 @@
+// skip: == not implemented yet
+
+io.write(123.toString == "123") // expect: true
+io.write(-123.toString == "-123") // expect: true
+io.write(-0.toString == "0") // expect: true
+
+// TODO(bob): Floating point numbers.
diff --git a/test/string_to_string.wren b/test/string_to_string.wren
new file mode 100644
index 00000000..81b1b635
--- /dev/null
+++ b/test/string_to_string.wren
@@ -0,0 +1,4 @@
+// skip: == not implemented yet
+
+io.write("".toString == "") // expect: true
+io.write("blah".toString == "blah") // expect: true