diff --git a/lib/collection.dart b/lib/collection.dart
index 612508b..31394f5 100644
--- a/lib/collection.dart
+++ b/lib/collection.dart
@@ -10,6 +10,7 @@ export "src/equality_map.dart";
 export "src/equality_set.dart";
 export "src/functions.dart";
 export "src/iterable_zip.dart";
+export "src/multi_map.dart";
 export "src/priority_queue.dart";
 export "src/queue_list.dart";
 export "src/union_set.dart";
diff --git a/lib/src/multi_map.dart b/lib/src/multi_map.dart
new file mode 100755
index 0000000..1173b3b
--- /dev/null
+++ b/lib/src/multi_map.dart
@@ -0,0 +1,367 @@
+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+import "dart:collection";
+import 'dart:convert';
+
+
+/**
+ * An implementation of [Map]. That allows for either the insertion of a value or
+ * a list of values for a given key.  Always returning either the value or the
+ * last value of the inserted list through the standard Map API.
+ * Additional method [multiple] allows access to the list of values for a given key.
+ *
+ * Default behavior is identical to [Map] with the exception that an unmodifiable
+ * Multimap cannot be constructed.
+ */
+class MultiMap<K, V> implements Map<K, V> {
+
+  LinkedHashMap<K, List<V>> _map;
+
+  /**
+   * Default constructor see [Map]
+   */
+  MultiMap({bool equals(K key1, K key2),
+  int hashCode(K key),
+  bool isValidKey(potentialKey)}) {
+    _map = new LinkedHashMap<K, List<V>>(equals:equals,hashCode:hashCode,isValidKey:isValidKey);
+  }
+
+  /**
+   * Factory constructing a Map from a parser generated Map literal.
+   * [elements] contains n key-value pairs.
+   * Todo: rwrozelle - How do we construct a multimap from a literal?
+   */
+  /*
+  factory MultiMap._fromLiteral(List elements) {
+    var map = new MultiMap<K, V>();
+    var len = elements.length;
+    for (int i = 1; i < len; i += 2) {
+      map[elements[i - 1]] = elements[i];
+    }
+    return map;
+  }
+  */
+
+  /**
+   * Unmodifiable constructor is not implemented due to class hierarchy mismatch.
+   * Todo:  rwrozelle - Is it important enough to figure out an unmodifiable implmentation?
+   */
+  /*
+  factory MultiMap.unmodifiable(Map other) {
+  }
+  */
+
+  /**
+   * Creates an identity-based map. See [Map]
+   */
+   factory MultiMap.identity() {
+     return new MultiMap<K, V>(equals:identical,hashCode:identityHashCode);
+   }
+
+  /**
+   * Creates a MultiMap that contains all key value pairs of [other].
+   */
+  factory MultiMap.from(Map other) {
+    MultiMap<K, V> result = new MultiMap<K, V>();
+    other.forEach((k, v)
+    {
+      result[k] = v;
+    });
+    return result;
+  }
+
+  /**
+   * Creates a MultiMap where the keys and values are computed from the
+   * [iterable].  See [Map]
+   */
+  factory MultiMap.fromIterable(Iterable iterable,
+      {K key(element), V value(element)}) {
+    MultiMap<K, V> map = new MultiMap<K, V>();
+    MultiMapHelper._fillMapWithMappedIterable(map, iterable, key, value);
+    return map;
+  }
+
+  /**
+   * Creates a MultiMap associating the given [keys] to [values].  See [Map]
+   */
+  factory MultiMap.fromIterables(Iterable<K> keys, Iterable<Object> values) {
+    MultiMap<K, V> map = new MultiMap<K, V>();
+    MultiMapHelper._fillMapWithIterables(map, keys, values);
+    return map;
+  }
+
+  /**
+   * Returns true if this map contains the given [value].
+   *
+   * Returns true if any of the values or last of list of values inserted in the
+   * map are equal to `value` according to the `==` operator.
+   */
+  bool containsValue(Object value) {
+    for (K key in keys) {
+      if (this[key] == value) return true;
+    }
+    return false;
+  }
+
+  /**
+   * Returns true if this map contains the given [key].
+   *
+   * Returns true if any of the keys in the map are equal to `key`
+   * according to the equality used by the map.
+   */
+  bool containsKey(Object key) => _map.containsKey(key);
+
+  /**
+   * Returns the value or last of list of values for the given [key] or null if [key]
+   * is not in the map.  See [Map] for what a return of 'null' means
+   */
+  V operator [](Object key) {
+    Object listValue = _map[key];
+    if (listValue == null || (listValue as List<V>).isEmpty) return null;
+    return (listValue as List<V>).last;
+  }
+
+  /**
+   * Associates the [key] with the given [value].
+   *
+   * The associated value (or list of values)
+   * is added or overwritten in the map.  If the [value] provided is a List<V>,
+   * the last value in this list is considered the "value" for standard Map API
+   */
+  void operator []=(K key, Object value) {
+    if (value is List<V>) {
+      _map[key] = value;
+    }
+    else if (value is V) {
+      //List<V> listValue = _map[key];
+      //if (listValue != null) listValue.add(value);
+      //else
+      _map[key] = [value];
+    }
+  }
+
+  /**
+   * Look up the value of [key], or add a new value if it isn't there.
+   * see [Map].
+   */
+  V putIfAbsent(key, ifAbsent()) {
+    if (containsKey(key)) return this[key];
+    var value = ifAbsent();
+    this[key] = value;
+    return value;
+  }
+
+  /**
+   * Adds all key-value pairs of [other] to this map.
+   *
+   * If a key of [other] is already in this map, its value is inserted.
+   *
+   * The operation is equivalent to doing `this[key] = value` for each key
+   * and associated value in other. It iterates over [other], which must
+   * therefore not change during the iteration.
+   */
+  void addAll(Map<K, V> other) {
+    for (K key in other.keys) {
+      this[key] = other[key];
+    }
+  }
+
+  /**
+   * Removes [key] and its associated value(s), if present, from the map.
+   *
+   * Returns the value or last of list of values associated with `key` before it
+   * was removed.  Returns `null` if `key` was not in the map.
+   *
+   * Note that values can be `null` and a returned `null` value doesn't
+   * always mean that the key was absent.
+   */
+  V remove(Object key) {
+    List<V> result = _map.remove(key);
+    if (result == null || result.isEmpty) return null;
+    return result.last;
+  }
+
+  /**
+   * Removes all pairs from the map.
+   *
+   * After this, the map is empty.
+   */
+  void clear() => _map.clear();
+
+  /**
+   * Applies [f] to each key-value pair of the map.
+   *
+   * Calling `f` must not add or remove keys from the map.
+   */
+  void forEach(void f(K key, V value)) {
+    for (K key in keys) {
+      f(key, this[key]);
+    }
+  }
+
+  /**
+   * Applies [f] to each key-value pair of the map.  Value used by [f] is the
+   * list of values associated with the key
+   *
+   * Calling `f` must not add or remove keys from the map.
+   */
+  void forEachMultiple(void f(K key, List<V> value)) {
+    for (K key in keys) {
+      f(key, this.multiple(key));
+    }
+  }
+
+  /**
+   * The keys of [this].
+   *
+   * The returned iterable has efficient `length` and `contains` operations,
+   * based on [length] and [containsKey] of the map.
+   *
+   * The order of iteration is defined by the individual `Map` implementation,
+   * but must be consistent between changes to the map.
+   *
+   * Modifying the map while iterating the keys
+   * may break the iteration.
+   */
+  Iterable<K> get keys => _map.keys;
+
+  /**
+   * The values of [this].  This is either the value or last of a list of values
+   * associated with the key.
+   *
+   * The values are iterated in the order of their corresponding keys.
+   * This means that iterating [keys] and [values] in parallel will
+   * provided matching pairs of keys and values.
+   *
+   * The returned iterable has an efficient `length` method based on the
+   * [length] of the map. Its [Iterable.contains] method is based on
+   * `==` comparison.
+   *
+   * Modifying the map while iterating the
+   * values may break the iteration.
+   */
+  Iterable<V> get values {
+    Iterable<V> result = new List<V>();
+    for (K key in this.keys) {
+      (result as List<V>).add(this[key]);
+    }
+    return result;
+  }
+
+  /**
+   * The number of key-value pairs in the map.
+   */
+  int get length => _map.length;
+
+  /**
+   * Returns true if there is no key-value pair in the map.
+   */
+  bool get isEmpty => _map.isEmpty;
+
+  /**
+   * Returns true if there is at least one key-value pair in the map.
+   */
+  bool get isNotEmpty => _map.isNotEmpty;
+
+  /**
+   * Returns the values of the key as a list
+   */
+  List<V> multiple(K key) {
+    return _map[key];
+  }
+
+  /**
+   * Returns the [query] split into a map according to the rules
+   * specified for FORM post in the [HTML 4.01 specification section
+   * 17.13.4](http://www.w3.org/TR/REC-html40/interact/forms.html#h-17.13.4 "HTML 4.01 section 17.13.4").
+   * Each key and value in the returned map has been decoded. If the [query]
+   * is the empty string an empty map is returned.
+   *
+   * Keys in the query string that have no value are mapped to the
+   * empty string.
+   *
+   * Each query component will be decoded using [encoding]. The default encoding
+   * is UTF-8.
+   * This is a copy of dart-sdk core Uri.splitQueryString modified to return
+   * List<Strings> when parameter is duplicated, for example:
+   * "foo=bar&baz=bang&fi=fo&fi=fum" returns {"foo": "bar", "baz": "bang", "fi":["fo","fum"]}
+   */
+  static MultiMap<String, String> splitQueryString(String query, {Encoding encoding: UTF8}) {
+    MultiMap<String, String> mmap = new MultiMap<String, String>();
+    query.split("&").fold({}, (map, element) {
+      int index = element.indexOf("=");
+      if (index == -1) {
+        if (element != "") {
+          mmap[Uri.decodeQueryComponent(element, encoding: encoding)] = "";
+        }
+      } else if (index != 0) {
+        var key = element.substring(0, index);
+        var value = element.substring(index + 1);
+        var decodedKey = Uri.decodeQueryComponent(key, encoding: encoding);
+        var existing = mmap.multiple(decodedKey);
+        if (existing != null) {
+          existing.add(Uri.decodeQueryComponent(value, encoding: encoding));
+          mmap[decodedKey] = existing;
+        }
+        else {
+          mmap[decodedKey] = Uri.decodeQueryComponent(value, encoding: encoding);
+        }
+      }
+    });
+    return mmap;
+  }
+}
+
+/**
+ * Helper class which implements complex [Map] operations
+ * in term of basic ones ([Map.keys], [Map.operator []],
+ * [Map.operator []=] and [Map.remove].)  Not all methods are
+ * necessary to implement each particular operation.
+ * This was copied from /dart/lib/collection/maps.dart because of privacy in
+ * original location.
+ */
+class MultiMapHelper {
+
+  static _id(x) => x;
+
+  /**
+   * Fills a map with key/value pairs computed from [iterable].
+   *
+   * This method is used by Map classes in the named constructor fromIterable.
+   */
+  static void _fillMapWithMappedIterable(Map map, Iterable iterable,
+      key(element), value(element)) {
+    if (key == null) key = _id;
+    if (value == null) value = _id;
+
+    for (var element in iterable) {
+      map[key(element)] = value(element);
+    }
+  }
+
+  /**
+   * Fills a map by associating the [keys] to [values].
+   *
+   * This method is used by Map classes in the named constructor fromIterables.
+   */
+  static void _fillMapWithIterables(Map map, Iterable keys,
+      Iterable values) {
+    Iterator keyIterator = keys.iterator;
+    Iterator valueIterator = values.iterator;
+
+    bool hasNextKey = keyIterator.moveNext();
+    bool hasNextValue = valueIterator.moveNext();
+
+    while (hasNextKey && hasNextValue) {
+      map[keyIterator.current] = valueIterator.current;
+      hasNextKey = keyIterator.moveNext();
+      hasNextValue = valueIterator.moveNext();
+    }
+
+    if (hasNextKey || hasNextValue) {
+      throw new ArgumentError("Iterables do not have same length.");
+    }
+  }
+}
\ No newline at end of file
diff --git a/test/multi_map_test.dart b/test/multi_map_test.dart
new file mode 100644
index 0000000..6994e08
--- /dev/null
+++ b/test/multi_map_test.dart
@@ -0,0 +1,263 @@
+//import 'dart:collection';
+import 'package:test/test.dart';
+import '../lib/src/multi_map.dart';
+
+
+void main() {
+  test('default constructor', () {
+    MultiMap<String, String> map = new MultiMap<String, String>();
+    expect(map is MultiMap, equals(true));
+    expect(map is Map, equals(true));
+  });
+
+  /**
+   * Todo: Only needed if MultiMap can be instantiated from literal.
+   */
+  /*
+  test('literal constructor', () {
+    MultiMap<String, String> map = {'foo':'bar'};
+    expect(map['foo'],equals('bar'));
+  });
+  */
+
+  test('identity constructor', () {
+    MultiMap<String, String> map = new MultiMap<String, String>.identity();
+    expect(map is MultiMap, equals(true));
+  });
+
+  test('from constructor', () {
+    Map<String, Object> other = {'foo': 'bar', 'fi':['fo','fum']};
+    MultiMap<String, String> map = new MultiMap<String, String>.from(other);
+    expect(map is MultiMap, equals(true));
+    expect(map['foo'],equals('bar'));
+    expect(map['fi'],equals('fum'));
+    expect(map.multiple('fi'),equals(['fo','fum']));
+  });
+
+  test('fromIterable constructor', () {
+    List<int> list = [1, 2, 3];
+    Map<String, int> map = new MultiMap.fromIterable(list,
+        key: (item) => item.toString(),
+        value: (item) => item * item);
+
+    expect(map is MultiMap, equals(true));
+    expect(map['1'],equals(1));
+    expect(map['2'],equals(4));
+    expect(map['3'],equals(9));
+  });
+
+  test('fromIterables constructor', () {
+    Map<String, Object> other = {'foo': 'bar', 'fi':['fo','fum']};
+    MultiMap<String, String> map = new MultiMap<String, String>.fromIterables(other.keys, other.values);
+    expect(map is MultiMap, equals(true));
+    expect(map['foo'],equals('bar'));
+    expect(map['fi'],equals('fum'));
+    expect(map.multiple('fi'),equals(['fo','fum']));
+  });
+
+  test('containsValue', () {
+    MultiMap<String, String> map = new MultiMap<String,
+        String>();
+    expect(map.containsValue('b'), equals(false));
+    map['a'] = 'b';
+    expect(map.containsValue('b'), equals(true));
+    List<String> cd = ['c', 'd'];
+    map['b'] = cd;
+    expect(map.containsValue('b'), equals(true));
+    expect(map.containsValue('c'), equals(false));
+    expect(map.containsValue('d'), equals(true));
+    map['b'] = 'e';
+    expect(map.containsValue('b'), equals(true));
+    expect(map.containsValue('c'), equals(false));
+    expect(map.containsValue('d'), equals(false));
+    expect(map.containsValue('e'), equals(true));
+  });
+
+  test('containsKey', () {
+    MultiMap<String, String> map = new MultiMap<String,
+        String>();
+    expect(map.containsKey('a'), equals(false));
+    map['a'] = 'b';
+    expect(map.containsKey('a'), equals(true));
+    List<String> cd = ['c', 'd'];
+    map['b'] = cd;
+    expect(map.containsKey('a'), equals(true));
+    expect(map.containsKey('b'), equals(true));
+    map['c'] = 'e';
+    expect(map.containsKey('a'), equals(true));
+    expect(map.containsKey('b'), equals(true));
+    expect(map.containsKey('c'), equals(true));
+  });
+
+  test('[]=', () {
+    MultiMap<String, String> map = new MultiMap<String,
+        String>();
+    expect(map['a'], equals(null));
+    map['a'] = 'b';
+    expect(map['a'], equals('b'));
+    List<String> bc = ['b', 'c'];
+    map['a'] = bc;
+    expect(map['a'], equals('c'));
+    map['a'] = 'd';
+    expect(map['a'], equals('d'));
+  });
+
+  test('putIfAbsent', () {
+    MultiMap<int, int> map = new MultiMap<int, int>();
+    map.putIfAbsent(4, () {
+      map[5] = 5;
+      map[4] = -1;
+      return 4;
+    });
+    expect(map[4], equals(4));
+    map.putIfAbsent(4, (){return 25;});
+    expect(map[4], equals(4));
+    map.putIfAbsent(3, (){return 25;});
+    expect(map[3], equals(25));
+  });
+
+  test('addAll', () {
+    Map<String, Object> other = {'foo': 'bar', 'fi':['fo','fum']};
+    MultiMap<String, String> map = new MultiMap<String, String>();
+    map.addAll(other);
+    expect(map['foo'],equals('bar'));
+    expect(map['fi'],equals('fum'));
+    expect(map.multiple('fi'),equals(['fo','fum']));
+  });
+
+  test('remove', () {
+    Map<String, Object> other = {'foo': 'bar', 'fi':['fo','fum']};
+    MultiMap<String, String> map = new MultiMap<String, String>();
+    map.addAll(other);
+    expect(map.remove('foo'),equals('bar'));
+    expect(map['foo'],equals(null));
+    expect(map.containsKey('foo'),equals(false));
+
+    expect(map.remove('fi'),equals('fum'));
+    expect(map['fi'],equals(null));
+    expect(map.containsKey('fi'),equals(false));
+    expect(map.multiple('fi'),equals(null));
+  });
+
+  test('clear', () {
+    Map<String, Object> other = {'foo': 'bar', 'fi':['fo','fum']};
+    MultiMap<String, String> map = new MultiMap<String, String>();
+    map.addAll(other);
+    map.clear();
+    expect(map.length,equals(0));
+    expect(map.keys,equals([]));
+  });
+
+  test('forEach', () {
+    Map<String, Object> other = {'foo': 'bar', 'fi':['fo','fum']};
+    MultiMap<String, String> map = new MultiMap<String, String>();
+    map.addAll(other);
+
+    int i = 0;
+    map.forEach((String key, String value){
+      if (key == 'foo') {
+        expect(i,equals(0));
+        expect(value, equals('bar'));
+      }
+      if (key == 'fi') {
+        expect(i,equals(1));
+        expect(value, equals('fum'));
+      }
+      i++;
+    });
+  });
+
+  test('forEachMultiple', () {
+    Map<String, Object> other = {'foo': 'bar', 'fi':['fo','fum']};
+    MultiMap<String, String> map = new MultiMap<String, String>();
+    map.addAll(other);
+
+    int i = 0;
+    map.forEachMultiple((String key, List<String> value){
+      if (key == 'foo') {
+        expect(i,equals(0));
+        expect(value, equals(['bar']));
+      }
+      if (key == 'fi') {
+        expect(i,equals(1));
+        expect(value, equals(['fo','fum']));
+      }
+      i++;
+    });
+  });
+
+  test('get keys', () {
+    MultiMap<String, String> map = new MultiMap<String,
+        String>();
+    expect(map['a'], equals(null));
+    map['a'] = 'b';
+    List<String> cd = ['c', 'd'];
+    map['b'] = cd;
+    Iterable<String> keys = map.keys;
+    int i = 0;
+    for (String key in keys) {
+      if (i == 0) expect(key, equals('a'));
+      if (i == 1) expect(key, equals('b'));
+      i++;
+    }
+  });
+
+  test('get values', () {
+    MultiMap<String, String> map = new MultiMap<String,
+        String>();
+    expect(map['a'], equals(null));
+    map['a'] = 'b';
+    List<String> cd = ['c', 'd'];
+    map['b'] = cd;
+    Iterable<String> values = map.values;
+    int i = 0;
+    for (String value in values) {
+      if (i == 0) expect(value, equals('b'));
+      if (i == 1) expect(value, equals('d'));
+      i++;
+    }
+  });
+
+  test('length', () {
+    MultiMap<String, String> map = new MultiMap<String,
+        String>();
+    expect(map.length, equals(0));
+    map['a'] = 'b';
+    expect(map.length, equals(1));
+  });
+
+  test('isEmpty', () {
+    MultiMap<String, String> map = new MultiMap<String,
+        String>();
+    expect(map.isEmpty, equals(true));
+    map['a'] = 'b';
+    expect(map.isEmpty, equals(false));
+  });
+
+  test('isNotEmpty', () {
+    MultiMap<String, String> map = new MultiMap<String,
+        String>();
+    expect(map.isNotEmpty, equals(false));
+    map['a'] = 'b';
+    expect(map.isNotEmpty, equals(true));
+  });
+
+
+  test('multiple', () {
+    MultiMap<String, String> map = new MultiMap<String,
+        String>();
+    expect(map.multiple('a'), equals(null));
+    map['a'] = 'b';
+    expect(map.multiple('a'), equals(['b']));
+    List<String> cd = ['c', 'd'];
+    map['b'] = cd;
+    expect(map.multiple('b'), equals(['c', 'd']));
+    map['b'] = 'e';
+    expect(map.multiple('b'), equals(['e']));
+
+    List<String> cdprime = ['c', 'd'];
+    map['b'] = cdprime;
+    expect(map.multiple('b'), equals(['c', 'd']));
+
+  });
+}
\ No newline at end of file