diff --git a/src/Microsoft.AspNet.Mvc.Common/PropertyHelper.cs b/src/Microsoft.AspNet.Mvc.Common/PropertyHelper.cs
index 2f2c9c9a4f..0cbf72779c 100644
--- a/src/Microsoft.AspNet.Mvc.Common/PropertyHelper.cs
+++ b/src/Microsoft.AspNet.Mvc.Common/PropertyHelper.cs
@@ -3,7 +3,7 @@
 
 using System;
 using System.Collections.Concurrent;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Linq;
 using System.Reflection;
 
@@ -84,12 +84,12 @@ namespace Microsoft.AspNet.Mvc
         /// </remarks>
         public static Func<object, object> MakeFastPropertyGetter(PropertyInfo propertyInfo)
         {
-            Contract.Assert(propertyInfo != null);
+            Debug.Assert(propertyInfo != null);
 
             var getMethod = propertyInfo.GetMethod;
-            Contract.Assert(getMethod != null);
-            Contract.Assert(!getMethod.IsStatic);
-            Contract.Assert(getMethod.GetParameters().Length == 0);
+            Debug.Assert(getMethod != null);
+            Debug.Assert(!getMethod.IsStatic);
+            Debug.Assert(getMethod.GetParameters().Length == 0);
 
             // Instance methods in the CLR can be turned into static methods where the first parameter
             // is open over "target". This parameter is always passed by reference, so we have a code
@@ -135,15 +135,15 @@ namespace Microsoft.AspNet.Mvc
         /// </remarks>
         public static Action<object, object> MakeFastPropertySetter(PropertyInfo propertyInfo)
         {
-            Contract.Assert(propertyInfo != null);
-            Contract.Assert(!propertyInfo.DeclaringType.GetTypeInfo().IsValueType);
+            Debug.Assert(propertyInfo != null);
+            Debug.Assert(!propertyInfo.DeclaringType.GetTypeInfo().IsValueType);
 
             var setMethod = propertyInfo.SetMethod;
-            Contract.Assert(setMethod != null);
-            Contract.Assert(!setMethod.IsStatic);
-            Contract.Assert(setMethod.ReturnType == typeof(void));
+            Debug.Assert(setMethod != null);
+            Debug.Assert(!setMethod.IsStatic);
+            Debug.Assert(setMethod.ReturnType == typeof(void));
             var parameters = setMethod.GetParameters();
-            Contract.Assert(parameters.Length == 1);
+            Debug.Assert(parameters.Length == 1);
 
             // Instance methods in the CLR can be turned into static methods where the first parameter
             // is open over "target". This parameter is always passed by reference, so we have a code
diff --git a/src/Microsoft.AspNet.Mvc.Core/AntiForgery/AntiForgeryTokenStore.cs b/src/Microsoft.AspNet.Mvc.Core/AntiForgery/AntiForgeryTokenStore.cs
index 224d99544c..c8c5330578 100644
--- a/src/Microsoft.AspNet.Mvc.Core/AntiForgery/AntiForgeryTokenStore.cs
+++ b/src/Microsoft.AspNet.Mvc.Core/AntiForgery/AntiForgeryTokenStore.cs
@@ -2,7 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Http;
 using Microsoft.Framework.DependencyInjection;
@@ -58,7 +58,7 @@ namespace Microsoft.AspNet.Mvc
             // Add the cookie to the request based context.
             // This is useful if the cookie needs to be reloaded in the context of the same request.
             var contextAccessor = httpContext.RequestServices.GetRequiredService<IContextAccessor<AntiForgeryContext>>();
-            Contract.Assert(contextAccessor.Value == null, "AntiForgeryContext should be set only once per request.");
+            Debug.Assert(contextAccessor.Value == null, "AntiForgeryContext should be set only once per request.");
             contextAccessor.SetValue(new AntiForgeryContext() { CookieToken = token });
 
             var serializedToken = _serializer.Serialize(token);
diff --git a/src/Microsoft.AspNet.Mvc.Core/AntiForgery/AntiForgeryWorker.cs b/src/Microsoft.AspNet.Mvc.Core/AntiForgery/AntiForgeryWorker.cs
index 34c22385ff..3f0cec6d79 100644
--- a/src/Microsoft.AspNet.Mvc.Core/AntiForgery/AntiForgeryWorker.cs
+++ b/src/Microsoft.AspNet.Mvc.Core/AntiForgery/AntiForgeryWorker.cs
@@ -2,8 +2,8 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
-using System.Diagnostics.Contracts;
 using System.Security.Claims;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Http;
@@ -152,7 +152,7 @@ namespace Microsoft.AspNet.Mvc
                 oldCookieToken = newCookieToken = _generator.GenerateCookieToken();
             }
 
-            Contract.Assert(_validator.IsCookieTokenValid(oldCookieToken));
+            Debug.Assert(_validator.IsCookieTokenValid(oldCookieToken));
 
             var formToken = _generator.GenerateFormToken(
                 httpContext,
diff --git a/src/Microsoft.AspNet.Mvc.Core/AntiForgery/BinaryBlob.cs b/src/Microsoft.AspNet.Mvc.Core/AntiForgery/BinaryBlob.cs
index 2e960d9c37..2bc8c9859c 100644
--- a/src/Microsoft.AspNet.Mvc.Core/AntiForgery/BinaryBlob.cs
+++ b/src/Microsoft.AspNet.Mvc.Core/AntiForgery/BinaryBlob.cs
@@ -4,7 +4,6 @@
 using System;
 using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
-using System.Diagnostics.Contracts;
 using System.Globalization;
 using System.Runtime.CompilerServices;
 using System.Security.Cryptography;
@@ -75,7 +74,7 @@ namespace Microsoft.AspNet.Mvc
                 return false;
             }
 
-            Contract.Assert(this._data.Length == other._data.Length);
+            Debug.Assert(this._data.Length == other._data.Length);
             return AreByteArraysEqual(this._data, other._data);
         }
 
@@ -88,7 +87,7 @@ namespace Microsoft.AspNet.Mvc
         {
             // Since data should contain uniformly-distributed entropy, the
             // first 32 bits can serve as the hash code.
-            Contract.Assert(_data != null && _data.Length >= (32 / 8));
+            Debug.Assert(_data != null && _data.Length >= (32 / 8));
             return BitConverter.ToInt32(_data, 0);
         }
 
diff --git a/src/Microsoft.AspNet.Mvc.Core/AntiForgery/TokenProvider.cs b/src/Microsoft.AspNet.Mvc.Core/AntiForgery/TokenProvider.cs
index f179dae5f1..f1198e9b33 100644
--- a/src/Microsoft.AspNet.Mvc.Core/AntiForgery/TokenProvider.cs
+++ b/src/Microsoft.AspNet.Mvc.Core/AntiForgery/TokenProvider.cs
@@ -2,7 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Security.Claims;
 using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Mvc.Core;
@@ -37,7 +37,7 @@ namespace Microsoft.AspNet.Mvc
                                                   ClaimsIdentity identity,
                                                   AntiForgeryToken cookieToken)
         {
-            Contract.Assert(IsCookieTokenValid(cookieToken));
+            Debug.Assert(IsCookieTokenValid(cookieToken));
 
             var formToken = new AntiForgeryToken()
             {
diff --git a/src/Microsoft.AspNet.Mvc.Core/Description/DefaultApiDescriptionProvider.cs b/src/Microsoft.AspNet.Mvc.Core/Description/DefaultApiDescriptionProvider.cs
index 28e176e850..b293985f75 100644
--- a/src/Microsoft.AspNet.Mvc.Core/Description/DefaultApiDescriptionProvider.cs
+++ b/src/Microsoft.AspNet.Mvc.Core/Description/DefaultApiDescriptionProvider.cs
@@ -3,7 +3,7 @@
 
 using System;
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Linq;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Mvc.HeaderValueAbstractions;
@@ -246,7 +246,7 @@ namespace Microsoft.AspNet.Mvc.Description
             else
             {
                 // We will never call this method with templateParameter == null && parameterDescriptor == null
-                Contract.Assert(parameterDescriptor != null);
+                Debug.Assert(parameterDescriptor != null);
             }
 
             if (parameterDescription.Type != null)
diff --git a/src/Microsoft.AspNet.Mvc.Core/Extensions/IEnumerableExtensions.cs b/src/Microsoft.AspNet.Mvc.Core/Extensions/IEnumerableExtensions.cs
index 13dec4f567..93e5642c30 100644
--- a/src/Microsoft.AspNet.Mvc.Core/Extensions/IEnumerableExtensions.cs
+++ b/src/Microsoft.AspNet.Mvc.Core/Extensions/IEnumerableExtensions.cs
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Linq;
 
 namespace System.Collections.Generic
@@ -10,7 +10,7 @@ namespace System.Collections.Generic
     {
         public static T[] AsArray<T>(this IEnumerable<T> values)
         {
-            Contract.Assert(values != null);
+            Debug.Assert(values != null);
 
             var array = values as T[];
             if (array == null)
diff --git a/src/Microsoft.AspNet.Mvc.Core/FilterActionInvoker.cs b/src/Microsoft.AspNet.Mvc.Core/FilterActionInvoker.cs
index 6353c5d622..6c4732fc50 100644
--- a/src/Microsoft.AspNet.Mvc.Core/FilterActionInvoker.cs
+++ b/src/Microsoft.AspNet.Mvc.Core/FilterActionInvoker.cs
@@ -3,7 +3,7 @@
 
 using System;
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Linq;
 using System.Runtime.ExceptionServices;
 using System.Threading.Tasks;
@@ -110,7 +110,7 @@ namespace Microsoft.AspNet.Mvc
                 // pipeline.
                 await InvokeExceptionFilter();
 
-                Contract.Assert(_exceptionContext != null);
+                Debug.Assert(_exceptionContext != null);
                 if (_exceptionContext.Exception != null)
                 {
                     // Exception filters only run when there's an exception - unsetting it will short-circuit
@@ -124,7 +124,7 @@ namespace Microsoft.AspNet.Mvc
                 // pipeline.
                 await InvokeExceptionFilter();
 
-                Contract.Assert(_exceptionContext != null);
+                Debug.Assert(_exceptionContext != null);
                 if (_exceptionContext.Exception != null)
                 {
                     // Exception filters only run when there's an exception - unsetting it will short-circuit
@@ -139,21 +139,21 @@ namespace Microsoft.AspNet.Mvc
                 //
                 // 1) Call the filter (if we have an exception)
                 // 2) No-op (if we don't have an exception)
-                Contract.Assert(_exceptionContext == null);
+                Debug.Assert(_exceptionContext == null);
                 _exceptionContext = new ExceptionContext(ActionContext, _filters);
 
                 try
                 {
                     await InvokeActionAuthorizationFilters();
 
-                    Contract.Assert(_authorizationContext != null);
+                    Debug.Assert(_authorizationContext != null);
                     if (_authorizationContext.Result == null)
                     {
                         // Authorization passed, run authorization filters and the action
                         await InvokeActionMethodWithFilters();
 
                         // Action filters might 'return' an unahndled exception instead of throwing
-                        Contract.Assert(_actionExecutedContext != null);
+                        Debug.Assert(_actionExecutedContext != null);
                         if (_actionExecutedContext.Exception != null && !_actionExecutedContext.ExceptionHandled)
                         {
                             _exceptionContext.Exception = _actionExecutedContext.Exception;
@@ -182,8 +182,8 @@ namespace Microsoft.AspNet.Mvc
         private async Task InvokeAuthorizationFilter()
         {
             // We should never get here if we already have a result.
-            Contract.Assert(_authorizationContext != null);
-            Contract.Assert(_authorizationContext.Result == null);
+            Debug.Assert(_authorizationContext != null);
+            Debug.Assert(_authorizationContext.Result == null);
 
             var current = _cursor.GetNextFilter<IAuthorizationFilter, IAsyncAuthorizationFilter>();
             if (current.FilterAsync != null)
@@ -223,7 +223,7 @@ namespace Microsoft.AspNet.Mvc
 
         private async Task<ActionExecutedContext> InvokeActionMethodFilter()
         {
-            Contract.Assert(_actionExecutingContext != null);
+            Debug.Assert(_actionExecutingContext != null);
             if (_actionExecutingContext.Result != null)
             {
                 // If we get here, it means that an async filter set a result AND called next(). This is forbidden.
@@ -298,7 +298,7 @@ namespace Microsoft.AspNet.Mvc
             _resultExecutingContext = new ResultExecutingContext(ActionContext, _filters, result);
             await InvokeActionResultFilter();
 
-            Contract.Assert(_resultExecutingContext != null);
+            Debug.Assert(_resultExecutingContext != null);
             if (_resultExecutedContext.Exception != null && !_resultExecutedContext.ExceptionHandled)
             {
                 // There's an unhandled exception in filters
@@ -315,7 +315,7 @@ namespace Microsoft.AspNet.Mvc
 
         private async Task<ResultExecutedContext> InvokeActionResultFilter()
         {
-            Contract.Assert(_resultExecutingContext != null);
+            Debug.Assert(_resultExecutingContext != null);
             if (_resultExecutingContext.Cancel == true)
             {
                 // If we get here, it means that an async filter set cancel == true AND called next().
@@ -383,7 +383,7 @@ namespace Microsoft.AspNet.Mvc
                 {
                     await InvokeActionResult();
 
-                    Contract.Assert(_resultExecutedContext == null);
+                    Debug.Assert(_resultExecutedContext == null);
                     _resultExecutedContext = new ResultExecutedContext(
                         _resultExecutingContext,
                         _filters,
diff --git a/src/Microsoft.AspNet.Mvc.Core/Filters/DefaultFilterProvider.cs b/src/Microsoft.AspNet.Mvc.Core/Filters/DefaultFilterProvider.cs
index 69a7b2e42d..ab1b7f4d85 100644
--- a/src/Microsoft.AspNet.Mvc.Core/Filters/DefaultFilterProvider.cs
+++ b/src/Microsoft.AspNet.Mvc.Core/Filters/DefaultFilterProvider.cs
@@ -2,7 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using Microsoft.AspNet.Mvc.Core;
 using Microsoft.Framework.DependencyInjection;
 
@@ -97,8 +97,8 @@ namespace Microsoft.AspNet.Mvc.Filters
 
         private void ApplyFilterToContainer(object actualFilter, IFilter filterMetadata)
         {
-            Contract.Assert(actualFilter != null, "actualFilter should not be null");
-            Contract.Assert(filterMetadata != null, "filterMetadata should not be null");
+            Debug.Assert(actualFilter != null, "actualFilter should not be null");
+            Debug.Assert(filterMetadata != null, "filterMetadata should not be null");
 
             var container = actualFilter as IFilterContainer;
 
diff --git a/src/Microsoft.AspNet.Mvc.Core/MvcRouteHandler.cs b/src/Microsoft.AspNet.Mvc.Core/MvcRouteHandler.cs
index e432d4736d..6c3cfdd8d9 100644
--- a/src/Microsoft.AspNet.Mvc.Core/MvcRouteHandler.cs
+++ b/src/Microsoft.AspNet.Mvc.Core/MvcRouteHandler.cs
@@ -2,7 +2,7 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Mvc.Core;
@@ -36,7 +36,7 @@ namespace Microsoft.AspNet.Mvc
             // users understand they should call the per request scoped middleware
             // or set HttpContext.Services manually
             var services = context.HttpContext.RequestServices;
-            Contract.Assert(services != null);
+            Debug.Assert(services != null);
 
             // Verify if AddMvc was done before calling UseMvc
             // We use the MvcMarkerService to make sure if all the services were added.
@@ -92,7 +92,7 @@ namespace Microsoft.AspNet.Mvc
         private async Task InvokeActionAsync(RouteContext context, ActionDescriptor actionDescriptor)
         {
             var services = context.HttpContext.RequestServices;
-            Contract.Assert(services != null);
+            Debug.Assert(services != null);
 
             var actionContext = new ActionContext(context.HttpContext, context.RouteData, actionDescriptor);
 
diff --git a/src/Microsoft.AspNet.Mvc.Core/Rendering/Html/DefaultHtmlGenerator.cs b/src/Microsoft.AspNet.Mvc.Core/Rendering/Html/DefaultHtmlGenerator.cs
index 7a46c84174..a5f6efd435 100644
--- a/src/Microsoft.AspNet.Mvc.Core/Rendering/Html/DefaultHtmlGenerator.cs
+++ b/src/Microsoft.AspNet.Mvc.Core/Rendering/Html/DefaultHtmlGenerator.cs
@@ -4,7 +4,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Globalization;
 using System.Linq;
 using System.Net;
@@ -96,7 +96,7 @@ namespace Microsoft.AspNet.Mvc.Rendering
             if (metadata != null)
             {
                 // CheckBoxFor() case. That API does not support passing isChecked directly.
-                Contract.Assert(!isChecked.HasValue);
+                Debug.Assert(!isChecked.HasValue);
 
                 if (metadata.Model != null)
                 {
@@ -312,10 +312,10 @@ namespace Microsoft.AspNet.Mvc.Rendering
             else
             {
                 // RadioButtonFor() case. That API does not support passing isChecked directly.
-                Contract.Assert(!isChecked.HasValue);
+                Debug.Assert(!isChecked.HasValue);
 
                 // Need a value to determine isChecked.
-                Contract.Assert(value != null);
+                Debug.Assert(value != null);
 
                 var model = metadata.Model;
                 var valueString = Convert.ToString(value, CultureInfo.CurrentCulture);
diff --git a/src/Microsoft.AspNet.Mvc.Core/Routing/ActionSelectorDecisionTree.cs b/src/Microsoft.AspNet.Mvc.Core/Routing/ActionSelectorDecisionTree.cs
index 0b360bfd6c..cdfe78488c 100644
--- a/src/Microsoft.AspNet.Mvc.Core/Routing/ActionSelectorDecisionTree.cs
+++ b/src/Microsoft.AspNet.Mvc.Core/Routing/ActionSelectorDecisionTree.cs
@@ -4,7 +4,7 @@
 using System;
 using System.Collections.Generic;
 using System.ComponentModel;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using Microsoft.AspNet.Mvc.Internal.DecisionTree;
 
 namespace Microsoft.AspNet.Mvc.Routing
@@ -73,7 +73,7 @@ namespace Microsoft.AspNet.Mvc.Routing
                 }
                 else if (hasNonCatchAll)
                 {
-                    Contract.Assert(filtered != null);
+                    Debug.Assert(filtered != null);
                     filtered.Add(action);
                 }
                 else
diff --git a/src/Microsoft.AspNet.Mvc.Core/Routing/AttributeRoutePrecedence.cs b/src/Microsoft.AspNet.Mvc.Core/Routing/AttributeRoutePrecedence.cs
index 1f7b7e49d5..b8b09bf041 100644
--- a/src/Microsoft.AspNet.Mvc.Core/Routing/AttributeRoutePrecedence.cs
+++ b/src/Microsoft.AspNet.Mvc.Core/Routing/AttributeRoutePrecedence.cs
@@ -3,7 +3,6 @@
 
 using System;
 using System.Diagnostics;
-using System.Diagnostics.Contracts;
 using System.Linq;
 using Microsoft.AspNet.Routing.Template;
 
@@ -25,7 +24,7 @@ namespace Microsoft.AspNet.Mvc.Routing
                 var segment = template.Segments[i];
 
                 var digit = ComputeDigit(segment);
-                Contract.Assert(digit >= 0 && digit < 10);
+                Debug.Assert(digit >= 0 && digit < 10);
 
                 precedence += Decimal.Divide(digit, (decimal)Math.Pow(10, i));
             }
diff --git a/src/Microsoft.AspNet.Mvc.Core/UrlHelper.cs b/src/Microsoft.AspNet.Mvc.Core/UrlHelper.cs
index 34c045a6dd..15308bfb22 100644
--- a/src/Microsoft.AspNet.Mvc.Core/UrlHelper.cs
+++ b/src/Microsoft.AspNet.Mvc.Core/UrlHelper.cs
@@ -3,7 +3,7 @@
 
 using System;
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Linq;
 using Microsoft.AspNet.Http;
 using Microsoft.AspNet.Routing;
@@ -153,7 +153,7 @@ namespace Microsoft.AspNet.Mvc
         private string GenerateUrl(string protocol, string host, string path, string fragment)
         {
             // We should have a robust and centrallized version of this code. See HttpAbstractions#28
-            Contract.Assert(path != null);
+            Debug.Assert(path != null);
 
             var url = path;
             if (!string.IsNullOrEmpty(fragment))
diff --git a/src/Microsoft.AspNet.Mvc.Core/ViewComponents/DefaultViewComponentSelector.cs b/src/Microsoft.AspNet.Mvc.Core/ViewComponents/DefaultViewComponentSelector.cs
index c19c868d2d..c3b71029bb 100644
--- a/src/Microsoft.AspNet.Mvc.Core/ViewComponents/DefaultViewComponentSelector.cs
+++ b/src/Microsoft.AspNet.Mvc.Core/ViewComponents/DefaultViewComponentSelector.cs
@@ -3,7 +3,7 @@
 
 using System;
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Linq;
 using System.Reflection;
 using Microsoft.AspNet.Mvc.Core;
@@ -81,7 +81,7 @@ namespace Microsoft.AspNet.Mvc
                 Type = typeInfo.AsType(),
             };
 
-            Contract.Assert(!string.IsNullOrEmpty(candidate.FullName));
+            Debug.Assert(!string.IsNullOrEmpty(candidate.FullName));
             var separatorIndex = candidate.FullName.LastIndexOf(".");
             if (separatorIndex >= 0)
             {
diff --git a/src/Microsoft.AspNet.Mvc.ModelBinding/Binders/GenericModelBinder.cs b/src/Microsoft.AspNet.Mvc.ModelBinding/Binders/GenericModelBinder.cs
index 851f9c3de8..0c53344599 100644
--- a/src/Microsoft.AspNet.Mvc.ModelBinding/Binders/GenericModelBinder.cs
+++ b/src/Microsoft.AspNet.Mvc.ModelBinding/Binders/GenericModelBinder.cs
@@ -3,7 +3,7 @@
 
 using System;
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Reflection;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Mvc.ModelBinding.Internal;
@@ -90,9 +90,9 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
                                                  Type openBinderType,
                                                  Type modelType)
         {
-            Contract.Assert(supportedInterfaceType != null);
-            Contract.Assert(openBinderType != null);
-            Contract.Assert(modelType != null);
+            Debug.Assert(supportedInterfaceType != null);
+            Debug.Assert(openBinderType != null);
+            Debug.Assert(modelType != null);
 
             var modelTypeArguments = GetGenericBinderTypeArgs(supportedInterfaceType, modelType);
 
diff --git a/src/Microsoft.AspNet.Mvc.ModelBinding/Internal/CollectionExtensions.cs b/src/Microsoft.AspNet.Mvc.ModelBinding/Internal/CollectionExtensions.cs
index 652a0fe41d..5b269ef75e 100644
--- a/src/Microsoft.AspNet.Mvc.ModelBinding/Internal/CollectionExtensions.cs
+++ b/src/Microsoft.AspNet.Mvc.ModelBinding/Internal/CollectionExtensions.cs
@@ -3,7 +3,7 @@
 
 using System;
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 
 namespace Microsoft.AspNet.Mvc.ModelBinding.Internal
 {
@@ -15,7 +15,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding.Internal
         /// </summary>
         public static T[] ToArrayWithoutNulls<T>(this ICollection<T> collection) where T : class
         {
-            Contract.Assert(collection != null);
+            Debug.Assert(collection != null);
 
             var result = new T[collection.Count];
             var count = 0;
diff --git a/src/Microsoft.AspNet.Mvc.ModelBinding/Validation/DefaultBodyModelValidator.cs b/src/Microsoft.AspNet.Mvc.ModelBinding/Validation/DefaultBodyModelValidator.cs
index 41cf7fe32a..c0e576a23e 100644
--- a/src/Microsoft.AspNet.Mvc.ModelBinding/Validation/DefaultBodyModelValidator.cs
+++ b/src/Microsoft.AspNet.Mvc.ModelBinding/Validation/DefaultBodyModelValidator.cs
@@ -4,7 +4,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Linq;
 using System.Runtime.CompilerServices;
 using Microsoft.AspNet.Mvc.ModelBinding.Internal;
@@ -210,7 +210,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
 
         private static Type GetElementType(Type type)
         {
-            Contract.Assert(typeof(IEnumerable).IsAssignableFrom(type));
+            Debug.Assert(typeof(IEnumerable).IsAssignableFrom(type));
             if (type.IsArray)
             {
                 return type.GetElementType();
diff --git a/src/Microsoft.AspNet.Mvc.ModelBinding/ValueProviders/ReadableStringCollectionValueProvider.cs b/src/Microsoft.AspNet.Mvc.ModelBinding/ValueProviders/ReadableStringCollectionValueProvider.cs
index 18dcba91f3..0ce9ff5d3b 100644
--- a/src/Microsoft.AspNet.Mvc.ModelBinding/ValueProviders/ReadableStringCollectionValueProvider.cs
+++ b/src/Microsoft.AspNet.Mvc.ModelBinding/ValueProviders/ReadableStringCollectionValueProvider.cs
@@ -3,7 +3,7 @@
 
 using System;
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Globalization;
 using System.Threading.Tasks;
 using Microsoft.AspNet.Http;
@@ -85,7 +85,7 @@ namespace Microsoft.AspNet.Mvc.ModelBinding
         {
             if (_values == null)
             {
-                Contract.Assert(_valuesFactory != null);
+                Debug.Assert(_valuesFactory != null);
                 _values = await _valuesFactory();
             }
 
diff --git a/src/Microsoft.AspNet.Mvc.ModelBinding/project.json b/src/Microsoft.AspNet.Mvc.ModelBinding/project.json
index 74ee5165a6..91093fac9c 100644
--- a/src/Microsoft.AspNet.Mvc.ModelBinding/project.json
+++ b/src/Microsoft.AspNet.Mvc.ModelBinding/project.json
@@ -23,7 +23,6 @@
       "dependencies": {
         "System.Collections.Concurrent": "4.0.10-beta-*",
         "System.ComponentModel.TypeConverter": "4.0.0-beta-*",
-        "System.Diagnostics.Contracts": "4.0.0-beta-*",
         "System.Reflection.TypeExtensions": "4.0.0-beta-*",
         "System.Runtime.Serialization.Primitives": "4.0.0-beta-*",
         "System.Runtime.Serialization.Xml": "4.0.10-beta-*",
diff --git a/src/Microsoft.AspNet.Mvc.Razor.Host/project.json b/src/Microsoft.AspNet.Mvc.Razor.Host/project.json
index 99b616113a..0b7ef3cc78 100644
--- a/src/Microsoft.AspNet.Mvc.Razor.Host/project.json
+++ b/src/Microsoft.AspNet.Mvc.Razor.Host/project.json
@@ -19,7 +19,6 @@
         "aspnetcore50": {
             "dependencies": {
                 "System.Collections.Concurrent": "4.0.10-beta-*",
-                "System.Diagnostics.Contracts": "4.0.0-beta-*",
                 "Microsoft.Framework.Runtime.Interfaces": { "version": "1.0.0-*", "type": "build" }
             }
         }
diff --git a/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/CollectionExtensions.cs b/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/CollectionExtensions.cs
index c8d80c0048..f9d718e47f 100644
--- a/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/CollectionExtensions.cs
+++ b/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/CollectionExtensions.cs
@@ -4,7 +4,7 @@
 #if ASPNETCORE50
 
 using System.Collections.ObjectModel;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Linq;
 
 namespace System.Collections.Generic
@@ -19,7 +19,7 @@ namespace System.Collections.Generic
         /// </summary>
         public static T[] AppendAndReallocate<T>(this T[] array, T value)
         {
-            Contract.Assert(array != null);
+            Debug.Assert(array != null);
 
             int originalLength = array.Length;
             T[] newArray = new T[originalLength + 1];
@@ -34,7 +34,7 @@ namespace System.Collections.Generic
         /// </summary>
         public static T[] AsArray<T>(this IEnumerable<T> values)
         {
-            Contract.Assert(values != null);
+            Debug.Assert(values != null);
 
             T[] array = values as T[];
             if (array == null)
@@ -50,7 +50,7 @@ namespace System.Collections.Generic
         /// </summary>
         public static Collection<T> AsCollection<T>(this IEnumerable<T> enumerable)
         {
-            Contract.Assert(enumerable != null);
+            Debug.Assert(enumerable != null);
 
             Collection<T> collection = enumerable as Collection<T>;
             if (collection != null)
@@ -71,7 +71,7 @@ namespace System.Collections.Generic
         /// </summary>
         public static IList<T> AsIList<T>(this IEnumerable<T> enumerable)
         {
-            Contract.Assert(enumerable != null);
+            Debug.Assert(enumerable != null);
 
             IList<T> list = enumerable as IList<T>;
             if (list != null)
@@ -87,7 +87,7 @@ namespace System.Collections.Generic
         /// </summary>
         public static List<T> AsList<T>(this IEnumerable<T> enumerable)
         {
-            Contract.Assert(enumerable != null);
+            Debug.Assert(enumerable != null);
 
             List<T> list = enumerable as List<T>;
             if (list != null)
@@ -107,8 +107,8 @@ namespace System.Collections.Generic
         /// </summary>
         public static void RemoveFrom<T>(this List<T> list, int start)
         {
-            Contract.Assert(list != null);
-            Contract.Assert(start >= 0 && start <= list.Count);
+            Debug.Assert(list != null);
+            Debug.Assert(start >= 0 && start <= list.Count);
 
             list.RemoveRange(start, list.Count - start);
         }
@@ -118,8 +118,8 @@ namespace System.Collections.Generic
         /// </summary>
         public static T SingleDefaultOrError<T, TArg1>(this IList<T> list, Action<TArg1> errorAction, TArg1 errorArg1)
         {
-            Contract.Assert(list != null);
-            Contract.Assert(errorAction != null);
+            Debug.Assert(list != null);
+            Debug.Assert(errorAction != null);
 
             switch (list.Count)
             {
@@ -142,8 +142,8 @@ namespace System.Collections.Generic
         /// </summary>
         public static TMatch SingleOfTypeDefaultOrError<TInput, TMatch, TArg1>(this IList<TInput> list, Action<TArg1> errorAction, TArg1 errorArg1) where TMatch : class
         {
-            Contract.Assert(list != null);
-            Contract.Assert(errorAction != null);
+            Debug.Assert(list != null);
+            Debug.Assert(errorAction != null);
 
             TMatch result = null;
             for (int i = 0; i < list.Count; i++)
@@ -170,7 +170,7 @@ namespace System.Collections.Generic
         /// </summary>
         public static T[] ToArrayWithoutNulls<T>(this ICollection<T> collection) where T : class
         {
-            Contract.Assert(collection != null);
+            Debug.Assert(collection != null);
 
             T[] result = new T[collection.Count];
             int count = 0;
@@ -199,8 +199,8 @@ namespace System.Collections.Generic
         /// </summary>
         public static Dictionary<TKey, TValue> ToDictionaryFast<TKey, TValue>(this TValue[] array, Func<TValue, TKey> keySelector, IEqualityComparer<TKey> comparer)
         {
-            Contract.Assert(array != null);
-            Contract.Assert(keySelector != null);
+            Debug.Assert(array != null);
+            Debug.Assert(keySelector != null);
 
             Dictionary<TKey, TValue> dictionary = new Dictionary<TKey, TValue>(array.Length, comparer);
             for (int i = 0; i < array.Length; i++)
@@ -216,8 +216,8 @@ namespace System.Collections.Generic
         /// </summary>
         public static Dictionary<TKey, TValue> ToDictionaryFast<TKey, TValue>(this IList<TValue> list, Func<TValue, TKey> keySelector, IEqualityComparer<TKey> comparer)
         {
-            Contract.Assert(list != null);
-            Contract.Assert(keySelector != null);
+            Debug.Assert(list != null);
+            Debug.Assert(keySelector != null);
 
             TValue[] array = list as TValue[];
             if (array != null)
@@ -232,8 +232,8 @@ namespace System.Collections.Generic
         /// </summary>
         public static Dictionary<TKey, TValue> ToDictionaryFast<TKey, TValue>(this IEnumerable<TValue> enumerable, Func<TValue, TKey> keySelector, IEqualityComparer<TKey> comparer)
         {
-            Contract.Assert(enumerable != null);
-            Contract.Assert(keySelector != null);
+            Debug.Assert(enumerable != null);
+            Debug.Assert(keySelector != null);
 
             TValue[] array = enumerable as TValue[];
             if (array != null)
@@ -258,8 +258,8 @@ namespace System.Collections.Generic
         /// </summary>
         private static Dictionary<TKey, TValue> ToDictionaryFastNoCheck<TKey, TValue>(IList<TValue> list, Func<TValue, TKey> keySelector, IEqualityComparer<TKey> comparer)
         {
-            Contract.Assert(list != null);
-            Contract.Assert(keySelector != null);
+            Debug.Assert(list != null);
+            Debug.Assert(keySelector != null);
 
             int listCount = list.Count;
             Dictionary<TKey, TValue> dictionary = new Dictionary<TKey, TValue>(listCount, comparer);
diff --git a/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/DefaultContentNegotiator.cs b/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/DefaultContentNegotiator.cs
index d8d8c5e1cd..6e85b923c4 100644
--- a/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/DefaultContentNegotiator.cs
+++ b/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/DefaultContentNegotiator.cs
@@ -5,7 +5,7 @@
 
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Linq;
 using System.Net.Http.Headers;
 using System.Text;
@@ -451,7 +451,7 @@ namespace System.Net.Http.Formatting
 
         private static MediaTypeFormatter[] GetWritingFormatters(IEnumerable<MediaTypeFormatter> formatters)
         {
-            Contract.Assert(formatters != null);
+            Debug.Assert(formatters != null);
             MediaTypeFormatterCollection formatterCollection = formatters as MediaTypeFormatterCollection;
             return formatters.AsArray();
         }
diff --git a/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/MediaTypeHeaderValueExtensions.cs b/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/MediaTypeHeaderValueExtensions.cs
index beb2b7a6cf..5cf91922bf 100644
--- a/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/MediaTypeHeaderValueExtensions.cs
+++ b/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/MediaTypeHeaderValueExtensions.cs
@@ -6,7 +6,7 @@
 using Microsoft.AspNet.Mvc;
 using System.Collections.Generic;
 using System.Collections.ObjectModel;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Linq;
 using System.Net.Http.Headers;
 
@@ -49,7 +49,7 @@ namespace System.Net.Http.Formatting
         public static bool IsSubsetOf(this MediaTypeHeaderValue mediaType1, MediaTypeHeaderValue mediaType2, out MediaTypeHeaderValueRange mediaType2Range)
         {
             // Performance-sensitive
-            Contract.Assert(mediaType1 != null);
+            Debug.Assert(mediaType1 != null);
 
             if (mediaType2 == null)
             {
diff --git a/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/MediaTypeWithQualityHeaderComparer.cs b/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/MediaTypeWithQualityHeaderComparer.cs
index 8ac2c8d48b..944a422dbd 100644
--- a/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/MediaTypeWithQualityHeaderComparer.cs
+++ b/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/MediaTypeWithQualityHeaderComparer.cs
@@ -4,7 +4,7 @@
 #if ASPNETCORE50
 
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Net.Http.Headers;
 
 namespace System.Net.Http.Formatting
@@ -38,8 +38,8 @@ namespace System.Net.Http.Formatting
         /// <returns></returns>
         public int Compare(MediaTypeWithQualityHeaderValue mediaType1, MediaTypeWithQualityHeaderValue mediaType2)
         {
-            Contract.Assert(mediaType1 != null, "The 'mediaType1' parameter should not be null.");
-            Contract.Assert(mediaType2 != null, "The 'mediaType2' parameter should not be null.");
+            Debug.Assert(mediaType1 != null, "The 'mediaType1' parameter should not be null.");
+            Debug.Assert(mediaType2 != null, "The 'mediaType2' parameter should not be null.");
 
             if (Object.ReferenceEquals(mediaType1, mediaType2))
             {
@@ -90,8 +90,8 @@ namespace System.Net.Http.Formatting
 
         private static int CompareBasedOnQualityFactor(MediaTypeWithQualityHeaderValue mediaType1, MediaTypeWithQualityHeaderValue mediaType2)
         {
-            Contract.Assert(mediaType1 != null);
-            Contract.Assert(mediaType2 != null);
+            Debug.Assert(mediaType1 != null);
+            Debug.Assert(mediaType2 != null);
 
             double mediaType1Quality = mediaType1.Quality ?? FormattingUtilities.Match;
             double mediaType2Quality = mediaType2.Quality ?? FormattingUtilities.Match;
diff --git a/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/ParsedMediaTypeHeaderValue.cs b/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/ParsedMediaTypeHeaderValue.cs
index d0b966789b..6e3f4c2214 100644
--- a/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/ParsedMediaTypeHeaderValue.cs
+++ b/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/ParsedMediaTypeHeaderValue.cs
@@ -3,7 +3,7 @@
 
 #if ASPNETCORE50
 
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Net.Http.Headers;
 
 namespace System.Net.Http.Formatting
@@ -21,10 +21,10 @@ namespace System.Net.Http.Formatting
 
         public ParsedMediaTypeHeaderValue(MediaTypeHeaderValue mediaTypeHeaderValue)
         {
-            Contract.Assert(mediaTypeHeaderValue != null);
+            Debug.Assert(mediaTypeHeaderValue != null);
             string mediaType = _mediaType = mediaTypeHeaderValue.MediaType;
             _delimiterIndex = mediaType.IndexOf(MediaTypeSubtypeDelimiter);
-            Contract.Assert(_delimiterIndex > 0, "The constructor of the MediaTypeHeaderValue would have failed if there wasn't a type and subtype.");
+            Debug.Assert(_delimiterIndex > 0, "The constructor of the MediaTypeHeaderValue would have failed if there wasn't a type and subtype.");
 
             _isAllMediaRange = false;
             _isSubtypeMediaRange = false;
diff --git a/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/StringWithQualityHeaderValueComparer.cs b/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/StringWithQualityHeaderValueComparer.cs
index 89a84a3a0e..a2c88fd244 100644
--- a/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/StringWithQualityHeaderValueComparer.cs
+++ b/src/Microsoft.AspNet.Mvc.WebApiCompatShim/ContentNegotiator/StringWithQualityHeaderValueComparer.cs
@@ -4,7 +4,7 @@
 #if ASPNETCORE50
 
 using System.Collections.Generic;
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Net.Http.Headers;
 
 namespace System.Net.Http.Formatting
@@ -43,8 +43,8 @@ namespace System.Net.Http.Formatting
         public int Compare(StringWithQualityHeaderValue stringWithQuality1,
                            StringWithQualityHeaderValue stringWithQuality2)
         {
-            Contract.Assert(stringWithQuality1 != null);
-            Contract.Assert(stringWithQuality2 != null);
+            Debug.Assert(stringWithQuality1 != null);
+            Debug.Assert(stringWithQuality2 != null);
 
             double quality1 = stringWithQuality1.Quality ?? FormattingUtilities.Match;
             double quality2 = stringWithQuality2.Quality ?? FormattingUtilities.Match;
diff --git a/src/Microsoft.AspNet.Mvc.WebApiCompatShim/HttpRequestMessage/HttpRequestMessageFeature.cs b/src/Microsoft.AspNet.Mvc.WebApiCompatShim/HttpRequestMessage/HttpRequestMessageFeature.cs
index 19f7d90591..90781a1909 100644
--- a/src/Microsoft.AspNet.Mvc.WebApiCompatShim/HttpRequestMessage/HttpRequestMessageFeature.cs
+++ b/src/Microsoft.AspNet.Mvc.WebApiCompatShim/HttpRequestMessage/HttpRequestMessageFeature.cs
@@ -1,7 +1,7 @@
 // Copyright (c) Microsoft Open Technologies, Inc. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-using System.Diagnostics.Contracts;
+using System.Diagnostics;
 using System.Net.Http;
 using Microsoft.AspNet.Http;
 
@@ -60,7 +60,7 @@ namespace Microsoft.AspNet.Mvc.WebApiCompatShim
                 if (!message.Headers.TryAddWithoutValidation(header.Key, header.Value))
                 {
                     var added = message.Content.Headers.TryAddWithoutValidation(header.Key, header.Value);
-                    Contract.Assert(added);
+                    Debug.Assert(added);
                 }
             }