diff --git a/src/csharp/Grpc.Auth/GoogleAuthInterceptors.cs b/src/csharp/Grpc.Auth/GoogleAuthInterceptors.cs
index 96d6ee87ae4..722b51f470c 100644
--- a/src/csharp/Grpc.Auth/GoogleAuthInterceptors.cs
+++ b/src/csharp/Grpc.Auth/GoogleAuthInterceptors.cs
@@ -33,6 +33,7 @@
 
 using System;
 using System.Threading;
+using System.Threading.Tasks;
 
 using Google.Apis.Auth.OAuth2;
 using Grpc.Core;
@@ -72,9 +73,10 @@ namespace Grpc.Auth
         public static AsyncAuthInterceptor FromAccessToken(string accessToken)
         {
             GrpcPreconditions.CheckNotNull(accessToken);
-            return new AsyncAuthInterceptor(async (context, metadata) =>
+            return new AsyncAuthInterceptor((context, metadata) =>
             {
                 metadata.Add(CreateBearerTokenHeader(accessToken));
+                return Task.FromResult<object>(null);
             });
         }
 
diff --git a/src/csharp/Grpc.Core/DefaultCallInvoker.cs b/src/csharp/Grpc.Core/DefaultCallInvoker.cs
index 1a99e41153b..b15aaefcd6a 100644
--- a/src/csharp/Grpc.Core/DefaultCallInvoker.cs
+++ b/src/csharp/Grpc.Core/DefaultCallInvoker.cs
@@ -102,6 +102,7 @@ namespace Grpc.Core
             return Calls.AsyncDuplexStreamingCall(call);
         }
 
+        /// <summary>Creates call invocation details for given method.</summary>
         protected virtual CallInvocationDetails<TRequest, TResponse> CreateCall<TRequest, TResponse>(Method<TRequest, TResponse> method, string host, CallOptions options)
                 where TRequest : class
                 where TResponse : class
diff --git a/src/csharp/Grpc.Core/GrpcEnvironment.cs b/src/csharp/Grpc.Core/GrpcEnvironment.cs
index 3ed2df203de..c57c904eb9d 100644
--- a/src/csharp/Grpc.Core/GrpcEnvironment.cs
+++ b/src/csharp/Grpc.Core/GrpcEnvironment.cs
@@ -59,7 +59,6 @@ namespace Grpc.Core
 
         static ILogger logger = new NullLogger();
 
-        readonly object myLock = new object();
         readonly GrpcThreadPool threadPool;
         readonly DebugStats debugStats = new DebugStats();
         readonly AtomicCounter cqPickerCounter = new AtomicCounter();
diff --git a/src/csharp/Grpc.Core/Internal/InterceptingCallInvoker.cs b/src/csharp/Grpc.Core/Internal/InterceptingCallInvoker.cs
index ef48dc71212..0c63e2092a5 100644
--- a/src/csharp/Grpc.Core/Internal/InterceptingCallInvoker.cs
+++ b/src/csharp/Grpc.Core/Internal/InterceptingCallInvoker.cs
@@ -48,7 +48,7 @@ namespace Grpc.Core.Internal
         readonly Func<CallOptions, CallOptions> callOptionsInterceptor;
 
         /// <summary>
-        /// Initializes a new instance of the <see cref="Grpc.Core.InterceptingCallInvoker"/> class.
+        /// Initializes a new instance of the <see cref="Grpc.Core.Internal.InterceptingCallInvoker"/> class.
         /// </summary>
         public InterceptingCallInvoker(CallInvoker callInvoker,
             Func<string, string> hostInterceptor = null,
diff --git a/src/csharp/Grpc.Core/Internal/NativeMetadataCredentialsPlugin.cs b/src/csharp/Grpc.Core/Internal/NativeMetadataCredentialsPlugin.cs
index 26af6311d52..b3714481eb2 100644
--- a/src/csharp/Grpc.Core/Internal/NativeMetadataCredentialsPlugin.cs
+++ b/src/csharp/Grpc.Core/Internal/NativeMetadataCredentialsPlugin.cs
@@ -78,7 +78,10 @@ namespace Grpc.Core.Internal
             {
                 var context = new AuthInterceptorContext(Marshal.PtrToStringAnsi(serviceUrlPtr),
                                                          Marshal.PtrToStringAnsi(methodNamePtr));
-                StartGetMetadata(context, callbackPtr, userDataPtr);
+                // Don't await, we are in a native callback and need to return.
+                #pragma warning disable 4014
+                GetMetadataAsync(context, callbackPtr, userDataPtr);
+                #pragma warning restore 4014
             }
             catch (Exception e)
             {
@@ -87,7 +90,7 @@ namespace Grpc.Core.Internal
             }
         }
 
-        private async Task StartGetMetadata(AuthInterceptorContext context, IntPtr callbackPtr, IntPtr userDataPtr)
+        private async Task GetMetadataAsync(AuthInterceptorContext context, IntPtr callbackPtr, IntPtr userDataPtr)
         {
             try
             {
diff --git a/src/csharp/Grpc.Core/Internal/UnmanagedLibrary.cs b/src/csharp/Grpc.Core/Internal/UnmanagedLibrary.cs
index 31e14028494..1553bdd687e 100644
--- a/src/csharp/Grpc.Core/Internal/UnmanagedLibrary.cs
+++ b/src/csharp/Grpc.Core/Internal/UnmanagedLibrary.cs
@@ -134,7 +134,11 @@ namespace Grpc.Core.Internal
             {
                 throw new MissingMethodException(string.Format("The native method \"{0}\" does not exist", methodName));
             }
-            return Marshal.GetDelegateForFunctionPointer(ptr, typeof(T)) as T;
+#if NETSTANDARD1_5
+            return Marshal.GetDelegateForFunctionPointer<T>(ptr);  // non-generic version is obsolete
+#else
+            return Marshal.GetDelegateForFunctionPointer(ptr, typeof(T)) as T;  // generic version not available in .NET45
+#endif
         }
 
         /// <summary>
diff --git a/src/csharp/Grpc.Core/Metadata.cs b/src/csharp/Grpc.Core/Metadata.cs
index 915bec146c9..e686f8e3980 100644
--- a/src/csharp/Grpc.Core/Metadata.cs
+++ b/src/csharp/Grpc.Core/Metadata.cs
@@ -95,11 +95,18 @@ namespace Grpc.Core
 
         #region IList members
 
+
+        /// <summary>
+        /// <see cref="T:IList`1"/>
+        /// </summary>
         public int IndexOf(Metadata.Entry item)
         {
             return entries.IndexOf(item);
         }
 
+        /// <summary>
+        /// <see cref="T:IList`1"/>
+        /// </summary>
         public void Insert(int index, Metadata.Entry item)
         {
             GrpcPreconditions.CheckNotNull(item);
@@ -107,12 +114,18 @@ namespace Grpc.Core
             entries.Insert(index, item);
         }
 
+        /// <summary>
+        /// <see cref="T:IList`1"/>
+        /// </summary>
         public void RemoveAt(int index)
         {
             CheckWriteable();
             entries.RemoveAt(index);
         }
 
+        /// <summary>
+        /// <see cref="T:IList`1"/>
+        /// </summary>
         public Metadata.Entry this[int index]
         {
             get
@@ -128,6 +141,9 @@ namespace Grpc.Core
             }
         }
 
+        /// <summary>
+        /// <see cref="T:IList`1"/>
+        /// </summary>
         public void Add(Metadata.Entry item)
         {
             GrpcPreconditions.CheckNotNull(item);
@@ -135,48 +151,75 @@ namespace Grpc.Core
             entries.Add(item);
         }
 
+        /// <summary>
+        /// <see cref="T:IList`1"/>
+        /// </summary>
         public void Add(string key, string value)
         {
             Add(new Entry(key, value));
         }
 
+        /// <summary>
+        /// <see cref="T:IList`1"/>
+        /// </summary>
         public void Add(string key, byte[] valueBytes)
         {
             Add(new Entry(key, valueBytes));
         }
 
+        /// <summary>
+        /// <see cref="T:IList`1"/>
+        /// </summary>
         public void Clear()
         {
             CheckWriteable();
             entries.Clear();
         }
 
+        /// <summary>
+        /// <see cref="T:IList`1"/>
+        /// </summary>
         public bool Contains(Metadata.Entry item)
         {
             return entries.Contains(item);
         }
 
+        /// <summary>
+        /// <see cref="T:IList`1"/>
+        /// </summary>
         public void CopyTo(Metadata.Entry[] array, int arrayIndex)
         {
             entries.CopyTo(array, arrayIndex);
         }
 
+        /// <summary>
+        /// <see cref="T:IList`1"/>
+        /// </summary>
         public int Count
         {
             get { return entries.Count; }
         }
 
+        /// <summary>
+        /// <see cref="T:IList`1"/>
+        /// </summary>
         public bool IsReadOnly
         {
             get { return readOnly; }
         }
 
+        /// <summary>
+        /// <see cref="T:IList`1"/>
+        /// </summary>
         public bool Remove(Metadata.Entry item)
         {
             CheckWriteable();
             return entries.Remove(item);
         }
 
+        /// <summary>
+        /// <see cref="T:IList`1"/>
+        /// </summary>
         public IEnumerator<Metadata.Entry> GetEnumerator()
         {
             return entries.GetEnumerator();