diff --git a/MessagePack.sln b/MessagePack.sln
index ba71e640..63cf2816 100644
--- a/MessagePack.sln
+++ b/MessagePack.sln
@@ -59,6 +59,8 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MessagePack.UniversalCodeGe
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MessagePack.AspNetCoreMvcFormatter.Tests", "tests\MessagePack.AspNetCoreMvcFormatter.Tests\MessagePack.AspNetCoreMvcFormatter.Tests.csproj", "{79C2B2CB-872A-4BA9-82DC-60F6DD77F940}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "MessagePack.Annotations", "src\MessagePack.Annotations\MessagePack.Annotations.csproj", "{85763F30-7733-44AB-89AB-D1B64F6E0D93}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -261,6 +263,18 @@ Global
 		{79C2B2CB-872A-4BA9-82DC-60F6DD77F940}.Release|x64.Build.0 = Release|Any CPU
 		{79C2B2CB-872A-4BA9-82DC-60F6DD77F940}.Release|x86.ActiveCfg = Release|Any CPU
 		{79C2B2CB-872A-4BA9-82DC-60F6DD77F940}.Release|x86.Build.0 = Release|Any CPU
+		{85763F30-7733-44AB-89AB-D1B64F6E0D93}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{85763F30-7733-44AB-89AB-D1B64F6E0D93}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{85763F30-7733-44AB-89AB-D1B64F6E0D93}.Debug|x64.ActiveCfg = Debug|Any CPU
+		{85763F30-7733-44AB-89AB-D1B64F6E0D93}.Debug|x64.Build.0 = Debug|Any CPU
+		{85763F30-7733-44AB-89AB-D1B64F6E0D93}.Debug|x86.ActiveCfg = Debug|Any CPU
+		{85763F30-7733-44AB-89AB-D1B64F6E0D93}.Debug|x86.Build.0 = Debug|Any CPU
+		{85763F30-7733-44AB-89AB-D1B64F6E0D93}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{85763F30-7733-44AB-89AB-D1B64F6E0D93}.Release|Any CPU.Build.0 = Release|Any CPU
+		{85763F30-7733-44AB-89AB-D1B64F6E0D93}.Release|x64.ActiveCfg = Release|Any CPU
+		{85763F30-7733-44AB-89AB-D1B64F6E0D93}.Release|x64.Build.0 = Release|Any CPU
+		{85763F30-7733-44AB-89AB-D1B64F6E0D93}.Release|x86.ActiveCfg = Release|Any CPU
+		{85763F30-7733-44AB-89AB-D1B64F6E0D93}.Release|x86.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE
@@ -282,9 +296,7 @@ Global
 		{2A32A538-BA26-4D89-85D0-E4249AFA0837} = {BF4C4202-5015-4FBD-80E6-D0F36A06F700}
 		{10AD85DD-929D-49B8-BD43-45242C2644B7} = {86309CF6-0054-4CE3-BFD3-CA0AA7DB17BC}
 		{79C2B2CB-872A-4BA9-82DC-60F6DD77F940} = {19FE674A-AC94-4E7E-B24C-2285D1D04CDE}
-	EndGlobalSection
-	GlobalSection(ExtensibilityGlobals) = postSolution
-		SolutionGuid = {26F0752B-06F7-44AD-BFEE-8F2E36B3AA27}
+		{85763F30-7733-44AB-89AB-D1B64F6E0D93} = {86309CF6-0054-4CE3-BFD3-CA0AA7DB17BC}
 	EndGlobalSection
 	GlobalSection(ExtensibilityGlobals) = postSolution
 		SolutionGuid = {B3911209-2DBF-47F8-98F6-BBC0EDFE63DE}
diff --git a/sandbox/DynamicCodeDumper/DynamicCodeDumper.csproj b/sandbox/DynamicCodeDumper/DynamicCodeDumper.csproj
index e36ad5ee..10e3522b 100644
--- a/sandbox/DynamicCodeDumper/DynamicCodeDumper.csproj
+++ b/sandbox/DynamicCodeDumper/DynamicCodeDumper.csproj
@@ -4,7 +4,7 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
   <ItemGroup>
-    <Compile Include="..\..\src\MessagePack\Attributes.cs">
+    <Compile Include="..\..\src\MessagePack.Annotations\Attributes.cs">
       <Link>Code\Attributes.cs</Link>
     </Compile>
     <Compile Include="..\..\src\MessagePack\FloatBits.cs">
@@ -19,7 +19,7 @@
     <Compile Include="..\..\src\MessagePack\IFormatterResolver.cs">
       <Link>Code\IFormatterResolver.cs</Link>
     </Compile>
-    <Compile Include="..\..\src\MessagePack\IMessagePackSerializationCallbackReceiver.cs">
+    <Compile Include="..\..\src\MessagePack.Annotations\IMessagePackSerializationCallbackReceiver.cs">
       <Link>Code\IMessagePackSerializationCallbackReceiver.cs</Link>
     </Compile>
     <Compile Include="..\..\src\MessagePack\Internal\AutomataDictionary.cs">
diff --git a/sandbox/PerfBenchmarkDotNet/PerfBenchmarkDotNet.csproj b/sandbox/PerfBenchmarkDotNet/PerfBenchmarkDotNet.csproj
index 7601d4f4..b556b76e 100644
--- a/sandbox/PerfBenchmarkDotNet/PerfBenchmarkDotNet.csproj
+++ b/sandbox/PerfBenchmarkDotNet/PerfBenchmarkDotNet.csproj
@@ -35,6 +35,9 @@
     <Content Include="MessagePack_1_6_0_3.dll" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="..\..\src\MessagePack.Annotations\MessagePack.Annotations.csproj">
+      <Aliases>newmsgpack</Aliases>
+    </ProjectReference>
     <ProjectReference Include="..\..\src\MessagePack\MessagePack.csproj">
       <Aliases>newmsgpack</Aliases>
     </ProjectReference>
diff --git a/src/MessagePack/Attributes.cs b/src/MessagePack.Annotations/Attributes.cs
similarity index 100%
rename from src/MessagePack/Attributes.cs
rename to src/MessagePack.Annotations/Attributes.cs
diff --git a/src/MessagePack/IMessagePackSerializationCallbackReceiver.cs b/src/MessagePack.Annotations/IMessagePackSerializationCallbackReceiver.cs
similarity index 100%
rename from src/MessagePack/IMessagePackSerializationCallbackReceiver.cs
rename to src/MessagePack.Annotations/IMessagePackSerializationCallbackReceiver.cs
diff --git a/src/MessagePack.Annotations/MessagePack.Annotations.csproj b/src/MessagePack.Annotations/MessagePack.Annotations.csproj
new file mode 100644
index 00000000..b208e5c2
--- /dev/null
+++ b/src/MessagePack.Annotations/MessagePack.Annotations.csproj
@@ -0,0 +1,14 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFrameworks>netstandard1.6;netstandard2.0;net45;net47</TargetFrameworks>
+    <NoWarn>$(NoWarn);CS0649</NoWarn>
+    <RootNamespace>MessagePack</RootNamespace>
+
+    <IsPackable>true</IsPackable>
+    <Title>MessagePack annotations for C#</Title>
+    <Description>Extremely Fast MessagePack(MsgPack) Serializer for C#(.NET, .NET Core, Unity, Xamarin).</Description>
+    <PackageTags>MsgPack;MessagePack;Serialization;Formatter;Serializer;Unity;Xamarin</PackageTags>
+  </PropertyGroup>
+
+</Project>
diff --git a/src/MessagePack.AspNetCoreMvcFormatter/MessagePack.AspNetCoreMvcFormatter.csproj b/src/MessagePack.AspNetCoreMvcFormatter/MessagePack.AspNetCoreMvcFormatter.csproj
index 0fc984b3..5314e5ef 100644
--- a/src/MessagePack.AspNetCoreMvcFormatter/MessagePack.AspNetCoreMvcFormatter.csproj
+++ b/src/MessagePack.AspNetCoreMvcFormatter/MessagePack.AspNetCoreMvcFormatter.csproj
@@ -15,6 +15,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\MessagePack\MessagePack.csproj" />
+    <ProjectReference Include="..\MessagePack.Annotations\MessagePack.Annotations.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/MessagePack.ImmutableCollection/MessagePack.ImmutableCollection.csproj b/src/MessagePack.ImmutableCollection/MessagePack.ImmutableCollection.csproj
index 0ab6a27c..e2fc2fdd 100644
--- a/src/MessagePack.ImmutableCollection/MessagePack.ImmutableCollection.csproj
+++ b/src/MessagePack.ImmutableCollection/MessagePack.ImmutableCollection.csproj
@@ -15,6 +15,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\MessagePack\MessagePack.csproj" />
+    <ProjectReference Include="..\MessagePack.Annotations\MessagePack.Annotations.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/MessagePack.ReactiveProperty/MessagePack.ReactiveProperty.csproj b/src/MessagePack.ReactiveProperty/MessagePack.ReactiveProperty.csproj
index be0c4c44..8c00cb01 100644
--- a/src/MessagePack.ReactiveProperty/MessagePack.ReactiveProperty.csproj
+++ b/src/MessagePack.ReactiveProperty/MessagePack.ReactiveProperty.csproj
@@ -21,6 +21,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\MessagePack\MessagePack.csproj" />
+    <ProjectReference Include="..\MessagePack.Annotations\MessagePack.Annotations.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/MessagePack.UnityShims/MessagePack.UnityShims.csproj b/src/MessagePack.UnityShims/MessagePack.UnityShims.csproj
index cdc0000c..e91f4536 100644
--- a/src/MessagePack.UnityShims/MessagePack.UnityShims.csproj
+++ b/src/MessagePack.UnityShims/MessagePack.UnityShims.csproj
@@ -14,6 +14,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\MessagePack\MessagePack.csproj" />
+    <ProjectReference Include="..\MessagePack.Annotations\MessagePack.Annotations.csproj" />
   </ItemGroup>
 
 </Project>
diff --git a/src/MessagePack/MessagePack.csproj b/src/MessagePack/MessagePack.csproj
index 604b742c..93ec0e40 100644
--- a/src/MessagePack/MessagePack.csproj
+++ b/src/MessagePack/MessagePack.csproj
@@ -29,6 +29,10 @@
     <PackageReference Include="System.ValueTuple" Version="4.5.0" />
   </ItemGroup>
 
+  <ItemGroup>
+    <ProjectReference Include="..\MessagePack.Annotations\MessagePack.Annotations.csproj" />
+  </ItemGroup>
+
   <ItemGroup>
     <None Update="Formatters\ForceSizePrimitiveFormatter.tt">
       <LastGenOutput>ForceSizePrimitiveFormatter.cs</LastGenOutput>