diff --git a/Mapper/CommandExtension.cs b/Mapper/CommandExtension.cs
index 504b6fc..6e7b174 100644
--- a/Mapper/CommandExtension.cs
+++ b/Mapper/CommandExtension.cs
@@ -109,11 +109,11 @@ public static async Task<Dictionary<TKey, TValue>> ToDictionaryAsync<TKey, TValu
         }
 
         /// <summary>Executes the <paramref name="cmd"/> and reads all the records in a lookup, grouped by key, using the supplied <paramref name="keyFunc"/> to generate the key</summary>
-        public static Lookup<TKey, TValue> ToLookup<TKey, TValue>(this IDbCommand cmd, Func<TValue, TKey> keyFunc)
+        public static HashLookup<TKey, TValue> ToLookup<TKey, TValue>(this IDbCommand cmd, Func<TValue, TKey> keyFunc)
         {
             Contract.Requires(cmd != null);
             Contract.Requires(keyFunc != null);
-            Contract.Ensures(Contract.Result<Lookup<TKey, TValue>>() != null);
+            Contract.Ensures(Contract.Result<HashLookup<TKey, TValue>>() != null);
             using (var reader = cmd.ExecuteReader())
             {
                 return reader.ToLookup(keyFunc);
@@ -121,11 +121,11 @@ public static Lookup<TKey, TValue> ToLookup<TKey, TValue>(this IDbCommand cmd, F
         }
 
         /// <summary>Executes the <paramref name="cmd"/> and reads all the records in a lookup, grouped by key, using the supplied <paramref name="keyFunc"/> to generate the key</summary>
-        public static async Task<Lookup<TKey, TValue>> ToLookupAsync<TKey, TValue>(this SqlCommand cmd, Func<TValue, TKey> keyFunc)
+        public static async Task<HashLookup<TKey, TValue>> ToLookupAsync<TKey, TValue>(this SqlCommand cmd, Func<TValue, TKey> keyFunc)
         {
             Contract.Requires(cmd != null);
             Contract.Requires(keyFunc != null);
-            Contract.Ensures(Contract.Result<Lookup<TKey, TValue>>() != null);
+            Contract.Ensures(Contract.Result<HashLookup<TKey, TValue>>() != null);
             using (var reader = await cmd.ExecuteReaderAsync())
             {
                 return await reader.ToLookupAsync(keyFunc);
diff --git a/Mapper/ConnectionExtension.cs b/Mapper/ConnectionExtension.cs
index 26ecb8b..0d9a6ab 100644
--- a/Mapper/ConnectionExtension.cs
+++ b/Mapper/ConnectionExtension.cs
@@ -185,13 +185,13 @@ public static ILookup<TKey, TValue> QueryLookup<TKey, TValue>(this IDbConnection
         }
 
         /// <summary>Executes a command using the <paramref name="sql"/> and reads all the records into a lookup</summary>
-        public static async Task<Lookup<TKey, TValue>> QueryLookupAsync<TKey, TValue>(this SqlConnection cnn, string sql, Func<TValue, TKey> keyFunc)
+        public static async Task<HashLookup<TKey, TValue>> QueryLookupAsync<TKey, TValue>(this SqlConnection cnn, string sql, Func<TValue, TKey> keyFunc)
         {
             Contract.Requires(cnn != null);
             Contract.Requires(cnn.State == ConnectionState.Open);
             Contract.Requires(!string.IsNullOrWhiteSpace(sql));
             Contract.Requires(keyFunc != null);
-            Contract.Ensures(Contract.Result<Lookup<TKey, TValue>>() != null);
+            Contract.Ensures(Contract.Result<HashLookup<TKey, TValue>>() != null);
             using (var cmd = cnn.CreateCommand())
             {
                 SetupCommand(cmd, cnn, sql, null);
@@ -200,14 +200,14 @@ public static async Task<Lookup<TKey, TValue>> QueryLookupAsync<TKey, TValue>(th
         }
 
         /// <summary>Executes a command using the <paramref name="sql"/> and <paramref name="parameters"/> and reads all the records into a lookup</summary>
-        public static async Task<Lookup<TKey, TValue>> QueryLookupAsync<TKey, TValue>(this SqlConnection cnn, string sql, object parameters, Func<TValue, TKey> keyFunc)
+        public static async Task<HashLookup<TKey, TValue>> QueryLookupAsync<TKey, TValue>(this SqlConnection cnn, string sql, object parameters, Func<TValue, TKey> keyFunc)
         {
             Contract.Requires(cnn != null);
             Contract.Requires(cnn.State == ConnectionState.Open);
             Contract.Requires(!string.IsNullOrWhiteSpace(sql));
             Contract.Requires(parameters != null);
             Contract.Requires(keyFunc != null);
-            Contract.Ensures(Contract.Result<Lookup<TKey, TValue>>() != null);
+            Contract.Ensures(Contract.Result<HashLookup<TKey, TValue>>() != null);
             using (var cmd = cnn.CreateCommand())
             {
                 SetupCommand(cmd, cnn, sql, parameters);
diff --git a/Mapper/DataReaderExtensions.cs b/Mapper/DataReaderExtensions.cs
index 2a38748..fc44a7c 100644
--- a/Mapper/DataReaderExtensions.cs
+++ b/Mapper/DataReaderExtensions.cs
@@ -131,13 +131,13 @@ public static async Task<Dictionary<TKey, TValue>> ToDictionaryAsync<TKey, TValu
         }
 
         /// <summary>Reads all the records in the lookup, group by key, using the supplied <paramref name="keyFunc"/> to generate the key</summary>
-        public static Lookup<TKey, TValue> ToLookup<TKey, TValue>(this IDataReader reader, Func<TValue, TKey> keyFunc)
+        public static HashLookup<TKey, TValue> ToLookup<TKey, TValue>(this IDataReader reader, Func<TValue, TKey> keyFunc)
         {
             Contract.Requires(reader != null);
             Contract.Requires(keyFunc != null);
             Contract.Requires(reader.IsClosed == false);
             var map = GetMappingFunc<TValue>(reader);
-            var lookup = new Lookup<TKey, TValue>();
+            var lookup = new HashLookup<TKey, TValue>();
             while (reader.Read())
             {
                 TValue value = map(reader);
@@ -148,13 +148,13 @@ public static Lookup<TKey, TValue> ToLookup<TKey, TValue>(this IDataReader reade
         }
 
         /// <summary>Reads all the records in the lookup, group by key, using the supplied <paramref name="keyFunc"/> to generate the key</summary>
-        public static async Task<Lookup<TKey, TValue>> ToLookupAsync<TKey, TValue>(this SqlDataReader reader, Func<TValue, TKey> keyFunc)
+        public static async Task<HashLookup<TKey, TValue>> ToLookupAsync<TKey, TValue>(this SqlDataReader reader, Func<TValue, TKey> keyFunc)
         {
             Contract.Requires(reader != null);
             Contract.Requires(keyFunc != null);
             Contract.Requires(reader.IsClosed == false);
             var map = GetMappingFunc<TValue>(reader);
-            var lookup = new Lookup<TKey, TValue>();
+            var lookup = new HashLookup<TKey, TValue>();
             while (await reader.ReadAsync())
             {
                 TValue value = map(reader);
diff --git a/Mapper/Lookup.cs b/Mapper/HashLookup.cs
similarity index 62%
rename from Mapper/Lookup.cs
rename to Mapper/HashLookup.cs
index e5cae63..dd61fb3 100644
--- a/Mapper/Lookup.cs
+++ b/Mapper/HashLookup.cs
@@ -13,7 +13,7 @@ namespace Mapper
     /// <summary>
     /// A key to many value dictionary data type
     /// </summary>
-    public class Lookup<TKey, TElement> : ILookup<TKey, TElement>
+    public class HashLookup<TKey, TElement> : ILookup<TKey, TElement>
     {
         private static readonly TElement[] Empty = new TElement[0];
         private readonly IEqualityComparer<TKey> _comparer;
@@ -21,17 +21,42 @@ public class Lookup<TKey, TElement> : ILookup<TKey, TElement>
         private Grouping<TKey, TElement> _lastGrouping;
         private int _count;
 
-        public Lookup(IEqualityComparer<TKey> comparer = null)
+        public HashLookup(IEqualityComparer<TKey> comparer = null)
         {
             _comparer = comparer ?? EqualityComparer<TKey>.Default;
             _groupings = new Grouping<TKey, TElement>[7];
         }
 
+        /// <summary>Gets the number of groupings (unique keys) in the <see cref="HashLookup{TKey,TElement}"/>.</summary>
+        /// <remarks>Does NOT return the number of items in the lookup</remarks>
         public int Count => _count;
 
-        public void Add(TKey key, TElement item)
+        /// <summary>
+        /// Add an <paramref name="element"/> to the lookup using supplied <paramref name="key"/>
+        /// </summary>
+        public void Add(TKey key, TElement element)
         {
-            GetGrouping(key, create: true).Add(item);
+            GetOrAddGrouping(key).Add(element);
+        }
+
+        /// <summary>
+        /// Add some <paramref name="items"/> to the lookup using the <paramref name="keyFunc"/> to get the key for each element
+        /// </summary>
+        public void AddRange(IEnumerable<TElement> items, Func<TElement, TKey> keyFunc)
+        {
+            Contract.Requires(items != null);
+            Contract.Requires(keyFunc != null);
+
+            TKey lastKey = default(TKey);
+            Grouping<TKey, TElement> grouping = null;
+            foreach (var element in items)
+            {
+                var key = keyFunc(element);
+                if (grouping == null || _comparer.Equals(key, lastKey) == false)
+                    grouping = GetOrAddGrouping(key);
+                grouping.Add(element);
+                lastKey = key;
+            }
         }
 
         /// <summary>Gets the <see cref="T:System.Collections.Generic.IEnumerable`1"/> sequence of values indexed by a specified key.</summary>
@@ -42,14 +67,20 @@ public IEnumerable<TElement> this[TKey key]
         {
             get
             {
-                Grouping<TKey, TElement> grouping = GetGrouping(key, create: false);
+                Contract.Ensures(Contract.Result<IEnumerable<TElement>>() != null);
+                int hashCode = InternalGetHashCode(key);
+                Grouping<TKey, TElement> grouping = FindGrouping(key, hashCode);
                 return grouping ?? (IEnumerable<TElement>) Empty;
             }
         }
 
+        /// <summary>
+        /// Determines whether a specified key exists in the <see cref="HashLookup{TKey,TElement}"/>.
+        /// </summary>
         public bool Contains(TKey key)
         {
-            return GetGrouping(key, create: false) != null;
+            int hashCode = InternalGetHashCode(key);
+            return FindGrouping(key, hashCode) != null;
         }
 
         public IEnumerator<IGrouping<TKey, TElement>> GetEnumerator()
@@ -77,20 +108,27 @@ internal int InternalGetHashCode(TKey key)
             return (key == null) ? 0 : _comparer.GetHashCode(key) & 0x7FFFFFFF;
         }
 
-        internal Grouping<TKey, TElement> GetGrouping(TKey key, bool create)
+        internal Grouping<TKey, TElement> GetOrAddGrouping(TKey key)
         {
             int hashCode = InternalGetHashCode(key);
-            for (Grouping<TKey, TElement> grouping = _groupings[hashCode % _groupings.Length]; grouping != null; grouping = grouping._hashNext)
+            var grouping = FindGrouping(key, hashCode);
+            return grouping ?? AddGrouping(key, hashCode);
+        }
+
+        private Grouping<TKey, TElement> FindGrouping(TKey key, int hashCode)
+        {
+            for (Grouping<TKey, TElement> grouping = _groupings[hashCode%_groupings.Length]; grouping != null; grouping = grouping._hashNext)
             {
                 if (grouping._hashCode == hashCode && _comparer.Equals(grouping._key, key))
                 {
                     return grouping;
                 }
             }
+            return null;
+        }
 
-            if (!create)
-                return null;
-
+        private Grouping<TKey, TElement> AddGrouping(TKey key, int hashCode)
+        {
             if (_count == _groupings.Length)
             {
                 Resize();
diff --git a/Mapper/Mapper.csproj b/Mapper/Mapper.csproj
index 5fad352..2f6fd5d 100644
--- a/Mapper/Mapper.csproj
+++ b/Mapper/Mapper.csproj
@@ -230,7 +230,7 @@
   </ItemGroup>
   <ItemGroup>
     <Compile Include="Grouping.cs" />
-    <Compile Include="Lookup.cs" />
+    <Compile Include="HashLookup.cs" />
     <Compile Include="Names.cs" />
     <Compile Include="SqlDataRecordExtensions.cs" />
     <Compile Include="CommandExtension.cs" />
diff --git a/Mapper/Mapper.nuspec b/Mapper/Mapper.nuspec
index 31b0f4a..6e31097 100644
--- a/Mapper/Mapper.nuspec
+++ b/Mapper/Mapper.nuspec
@@ -2,7 +2,7 @@
 <package >
   <metadata>
     <id>Mapper</id>
-    <version>1.0.1.0</version>
+    <version>1.0.1.1</version>
     <authors>BusterWood</authors>
     <description>A convention-based object cloner, object-object mapper (like AutoMapper), IDataReader to object mapper, object to IDbDataParameter mapper, etc.</description>
     <projectUrl>https://github.com/busterwood/mapper</projectUrl>
diff --git a/Mapper/Properties/AssemblyInfo.cs b/Mapper/Properties/AssemblyInfo.cs
index 5e68704..b327563 100644
--- a/Mapper/Properties/AssemblyInfo.cs
+++ b/Mapper/Properties/AssemblyInfo.cs
@@ -12,6 +12,6 @@
 [assembly: AssemblyCulture("")]
 [assembly: ComVisible(false)]
 [assembly: AssemblyVersion("1.0.0.0")]
-[assembly: AssemblyFileVersion("1.0.1.0")]
+[assembly: AssemblyFileVersion("1.0.1.1")]
 
 [assembly: InternalsVisibleTo("Mapper.UnitTests")]
\ No newline at end of file