diff --git a/builtin/core.wren b/builtin/core.wren
index 598f6168..34713981 100644
--- a/builtin/core.wren
+++ b/builtin/core.wren
@@ -89,8 +89,39 @@ class List is Sequence {
 }
 
 class Map {
-  // TODO: Implement this.
-  toString { "{}" }
+  keys { new MapKeySequence(this) }
+  values { new MapValueSequence(this) }
+
+  toString {
+    var first = true
+    var result = "{"
+
+    for (key in keys) {
+      if (!first) result = result + ", "
+      first = false
+      result = result + key.toString + ": " + this[key].toString
+    }
+
+    return result + "}"
+  }
+}
+
+class MapKeySequence is Sequence {
+  new(map) {
+    _map = map
+  }
+
+  iterate(n) { _map.iterate_(n) }
+  iteratorValue(iterator) { _map.keyIteratorValue_(iterator) }
+}
+
+class MapValueSequence is Sequence {
+  new(map) {
+    _map = map
+  }
+
+  iterate(n) { _map.iterate_(n) }
+  iteratorValue(iterator) { _map.valueIteratorValue_(iterator) }
 }
 
 class Range is Sequence {}
diff --git a/src/wren_core.c b/src/wren_core.c
index 9d77f55d..fe06e07b 100644
--- a/src/wren_core.c
+++ b/src/wren_core.c
@@ -132,8 +132,39 @@ static const char* libSource =
 "}\n"
 "\n"
 "class Map {\n"
-"  // TODO: Implement this.\n"
-"  toString { \"{}\" }\n"
+"  keys { new MapKeySequence(this) }\n"
+"  values { new MapValueSequence(this) }\n"
+"\n"
+"  toString {\n"
+"    var first = true\n"
+"    var result = \"{\"\n"
+"\n"
+"    for (key in keys) {\n"
+"      if (!first) result = result + \", \"\n"
+"      first = false\n"
+"      result = result + key.toString + \": \" + this[key].toString\n"
+"    }\n"
+"\n"
+"    return result + \"}\"\n"
+"  }\n"
+"}\n"
+"\n"
+"class MapKeySequence is Sequence {\n"
+"  new(map) {\n"
+"    _map = map\n"
+"  }\n"
+"\n"
+"  iterate(n) { _map.iterate_(n) }\n"
+"  iteratorValue(iterator) { _map.keyIteratorValue_(iterator) }\n"
+"}\n"
+"\n"
+"class MapValueSequence is Sequence {\n"
+"  new(map) {\n"
+"    _map = map\n"
+"  }\n"
+"\n"
+"  iterate(n) { _map.iterate_(n) }\n"
+"  iteratorValue(iterator) { _map.valueIteratorValue_(iterator) }\n"
 "}\n"
 "\n"
 "class Range is Sequence {}\n";
@@ -714,6 +745,62 @@ DEF_NATIVE(map_count)
   RETURN_NUM(AS_MAP(args[0])->count);
 }
 
+DEF_NATIVE(map_iterate)
+{
+  ObjMap* map = AS_MAP(args[0]);
+
+  if (map->count == 0) RETURN_FALSE;
+
+  // If we're starting the iteration, return the first entry.
+  int index = -1;
+  if (!IS_NULL(args[1]))
+  {
+    if (!validateInt(vm, args, 1, "Iterator")) return PRIM_ERROR;
+    index = (int)AS_NUM(args[1]);
+
+    if (index < 0 || index >= map->capacity) RETURN_FALSE;
+  }
+
+  // Find the next used entry, if any.
+  for (index++; index < map->capacity; index++)
+  {
+    if (!IS_UNDEFINED(map->entries[index].key)) RETURN_NUM(index);
+  }
+
+  // If we get here, walked all of the entries.
+  RETURN_FALSE;
+}
+
+DEF_NATIVE(map_keyIteratorValue)
+{
+  ObjMap* map = AS_MAP(args[0]);
+  int index = validateIndex(vm, args, map->capacity, 1, "Iterator");
+  if (index == -1) return PRIM_ERROR;
+
+  MapEntry* entry = &map->entries[index];
+  if (IS_UNDEFINED(entry->key))
+  {
+    RETURN_ERROR("Invalid map iterator value.");
+  }
+
+  RETURN_VAL(entry->key);
+}
+
+DEF_NATIVE(map_valueIteratorValue)
+{
+  ObjMap* map = AS_MAP(args[0]);
+  int index = validateIndex(vm, args, map->capacity, 1, "Iterator");
+  if (index == -1) return PRIM_ERROR;
+
+  MapEntry* entry = &map->entries[index];
+  if (IS_UNDEFINED(entry->key))
+  {
+    RETURN_ERROR("Invalid map iterator value.");
+  }
+
+  RETURN_VAL(entry->value);
+}
+
 DEF_NATIVE(null_not)
 {
   RETURN_VAL(TRUE_VAL);
@@ -1382,6 +1469,9 @@ void wrenInitializeCore(WrenVM* vm)
   NATIVE(vm->mapClass, "[ ]=", map_subscriptSetter);
   NATIVE(vm->mapClass, "clear", map_clear);
   NATIVE(vm->mapClass, "count", map_count);
+  NATIVE(vm->mapClass, "iterate_ ", map_iterate);
+  NATIVE(vm->mapClass, "keyIteratorValue_ ", map_keyIteratorValue);
+  NATIVE(vm->mapClass, "valueIteratorValue_ ", map_valueIteratorValue);
   // TODO: More map methods.
 
   vm->rangeClass = AS_CLASS(findGlobal(vm, "Range"));
diff --git a/test/map/key_iterate.wren b/test/map/key_iterate.wren
new file mode 100644
index 00000000..f1b169a0
--- /dev/null
+++ b/test/map/key_iterate.wren
@@ -0,0 +1,45 @@
+var a = {"one": 1, "two": 2, "three": 3, "four": 4}.keys
+
+// The precise numeric values aren't defined since they are indexes into the
+// entry table and the hashing process isn't specified. So we just validate
+// what we can assume about them.
+
+IO.print(a.iterate(null) is Num) // expect: true
+IO.print(a.iterate(null) >= 0) // expect: true
+
+IO.print(a.iterate(0) is Num) // expect: true
+IO.print(a.iterate(0) > 0) // expect: true
+IO.print(a.iterate(1) is Num) // expect: true
+IO.print(a.iterate(1) > 0) // expect: true
+IO.print(a.iterate(2) is Num) // expect: true
+IO.print(a.iterate(2) > 0) // expect: true
+IO.print(a.iterate(3) is Num) // expect: true
+IO.print(a.iterate(3) > 0) // expect: true
+
+var previous = -1
+var iterator = a.iterate(null)
+while (iterator) {
+  IO.print(iterator > previous)
+  IO.print(iterator is Num)
+  previous = iterator
+  iterator = a.iterate(iterator)
+}
+// First entry:
+// expect: true
+// expect: true
+// Second entry:
+// expect: true
+// expect: true
+// Third entry:
+// expect: true
+// expect: true
+// Fourth entry:
+// expect: true
+// expect: true
+
+// Out of bounds.
+IO.print(a.iterate(16)) // expect: false
+IO.print(a.iterate(-1)) // expect: false
+
+// Nothing to iterate in an empty map.
+IO.print({}.keys.iterate(null)) // expect: false
diff --git a/test/map/key_iterate_iterator_not_int.wren b/test/map/key_iterate_iterator_not_int.wren
new file mode 100644
index 00000000..56d21bc1
--- /dev/null
+++ b/test/map/key_iterate_iterator_not_int.wren
@@ -0,0 +1,2 @@
+var a = {1: 2, 3: 4}
+a.keys.iterate(1.5) // expect runtime error: Iterator must be an integer.
diff --git a/test/map/key_iterate_iterator_not_num.wren b/test/map/key_iterate_iterator_not_num.wren
new file mode 100644
index 00000000..f6d9193f
--- /dev/null
+++ b/test/map/key_iterate_iterator_not_num.wren
@@ -0,0 +1,2 @@
+var a = {1: 2, 3: 4}
+a.keys.iterate("2") // expect runtime error: Iterator must be a number.
diff --git a/test/map/to_string.wren b/test/map/to_string.wren
new file mode 100644
index 00000000..46b6b5b9
--- /dev/null
+++ b/test/map/to_string.wren
@@ -0,0 +1,27 @@
+// Handle empty map.
+IO.print({}.toString)             // expect: {}
+
+// Does not quote strings.
+IO.print({"1": "2"}.toString) // expect: {1: 2}
+
+// Nested maps.
+IO.print({1: {2: {}}}) // expect: {1: {2: {}}}
+
+// Calls toString on elements.
+class Foo {
+  toString { "Foo.toString" }
+}
+
+IO.print({1: new Foo}) // expect: {1: Foo.toString}
+
+// Since iteration order is unspecified, we don't know what order the results
+// will be.
+var s = {1: 2, 3: 4, 5: 6}.toString
+IO.print(s == "{1: 2, 3: 4, 5: 6}" ||
+         s == "{1: 2, 5: 6, 3: 4}" ||
+         s == "{3: 4, 1: 2, 5: 6}" ||
+         s == "{3: 4, 5: 6, 1: 2}" ||
+         s == "{5: 6, 1: 2, 3: 4}" ||
+         s == "{5: 6, 3: 4, 1: 2}") // expect: true
+
+// TODO: Handle maps that contain themselves.
\ No newline at end of file
diff --git a/test/map/value_iterate.wren b/test/map/value_iterate.wren
new file mode 100644
index 00000000..cf185abf
--- /dev/null
+++ b/test/map/value_iterate.wren
@@ -0,0 +1,45 @@
+var a = {"one": 1, "two": 2, "three": 3, "four": 4}.values
+
+// The precise numeric values aren't defined since they are indexes into the
+// entry table and the hashing process isn't specified. So we just validate
+// what we can assume about them.
+
+IO.print(a.iterate(null) is Num) // expect: true
+IO.print(a.iterate(null) >= 0) // expect: true
+
+IO.print(a.iterate(0) is Num) // expect: true
+IO.print(a.iterate(0) > 0) // expect: true
+IO.print(a.iterate(1) is Num) // expect: true
+IO.print(a.iterate(1) > 0) // expect: true
+IO.print(a.iterate(2) is Num) // expect: true
+IO.print(a.iterate(2) > 0) // expect: true
+IO.print(a.iterate(3) is Num) // expect: true
+IO.print(a.iterate(3) > 0) // expect: true
+
+var previous = -1
+var iterator = a.iterate(null)
+while (iterator) {
+  IO.print(iterator > previous)
+  IO.print(iterator is Num)
+  previous = iterator
+  iterator = a.iterate(iterator)
+}
+// First entry:
+// expect: true
+// expect: true
+// Second entry:
+// expect: true
+// expect: true
+// Third entry:
+// expect: true
+// expect: true
+// Fourth entry:
+// expect: true
+// expect: true
+
+// Out of bounds.
+IO.print(a.iterate(16)) // expect: false
+IO.print(a.iterate(-1)) // expect: false
+
+// Nothing to iterate in an empty map.
+IO.print({}.values.iterate(null)) // expect: false
diff --git a/test/map/value_iterate_iterator_not_int.wren b/test/map/value_iterate_iterator_not_int.wren
new file mode 100644
index 00000000..792cdaf4
--- /dev/null
+++ b/test/map/value_iterate_iterator_not_int.wren
@@ -0,0 +1,2 @@
+var a = {1: 2, 3: 4}
+a.values.iterate(1.5) // expect runtime error: Iterator must be an integer.
diff --git a/test/map/value_iterate_iterator_not_num.wren b/test/map/value_iterate_iterator_not_num.wren
new file mode 100644
index 00000000..dd2764a4
--- /dev/null
+++ b/test/map/value_iterate_iterator_not_num.wren
@@ -0,0 +1,2 @@
+var a = {1: 2, 3: 4}
+a.values.iterate("2") // expect runtime error: Iterator must be a number.