diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs
index 6c83ffe225776bc214b6421760fcd5aa1d9cb4f6..a7a7908f1f32e504405829ae8257ce84676a30e0 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.cs
@@ -8,11 +8,11 @@ namespace Microsoft.Extensions.Configuration
 {
     public static partial class ConfigurationExtensions
     {
-        public static Microsoft.Extensions.Configuration.IConfigurationBuilder Add<TSource>(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder, System.Action<TSource> configureSource) where TSource : Microsoft.Extensions.Configuration.IConfigurationSource, new() { throw null; }
-        public static System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, string>> AsEnumerable(this Microsoft.Extensions.Configuration.IConfiguration configuration) { throw null; }
-        public static System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, string>> AsEnumerable(this Microsoft.Extensions.Configuration.IConfiguration configuration, bool makePathsRelative) { throw null; }
-        public static bool Exists(this Microsoft.Extensions.Configuration.IConfigurationSection section) { throw null; }
-        public static string GetConnectionString(this Microsoft.Extensions.Configuration.IConfiguration configuration, string name) { throw null; }
+        public static Microsoft.Extensions.Configuration.IConfigurationBuilder Add<TSource>(this Microsoft.Extensions.Configuration.IConfigurationBuilder builder, System.Action<TSource>? configureSource) where TSource : Microsoft.Extensions.Configuration.IConfigurationSource, new() { throw null; }
+        public static System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, string?>> AsEnumerable(this Microsoft.Extensions.Configuration.IConfiguration configuration) { throw null; }
+        public static System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, string?>> AsEnumerable(this Microsoft.Extensions.Configuration.IConfiguration configuration, bool makePathsRelative) { throw null; }
+        public static bool Exists([System.Diagnostics.CodeAnalysis.NotNullWhen(true)] this Microsoft.Extensions.Configuration.IConfigurationSection? section) { throw null; }
+        public static string? GetConnectionString(this Microsoft.Extensions.Configuration.IConfiguration configuration, string name) { throw null; }
         public static Microsoft.Extensions.Configuration.IConfigurationSection GetRequiredSection(this Microsoft.Extensions.Configuration.IConfiguration configuration, string key) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Property)]
@@ -26,8 +26,9 @@ public static partial class ConfigurationPath
         public static readonly string KeyDelimiter;
         public static string Combine(System.Collections.Generic.IEnumerable<string> pathSegments) { throw null; }
         public static string Combine(params string[] pathSegments) { throw null; }
-        public static string GetParentPath(string path) { throw null; }
-        public static string GetSectionKey(string path) { throw null; }
+        public static string? GetParentPath(string? path) { throw null; }
+        [return: System.Diagnostics.CodeAnalysis.NotNullIfNotNull("path")]
+        public static string? GetSectionKey(string? path) { throw null; }
     }
     public static partial class ConfigurationRootExtensions
     {
@@ -35,7 +36,7 @@ public static partial class ConfigurationRootExtensions
     }
     public partial interface IConfiguration
     {
-        string this[string key] { get; set; }
+        string? this[string key] { get; set; }
         System.Collections.Generic.IEnumerable<Microsoft.Extensions.Configuration.IConfigurationSection> GetChildren();
         Microsoft.Extensions.Primitives.IChangeToken GetReloadToken();
         Microsoft.Extensions.Configuration.IConfigurationSection GetSection(string key);
@@ -49,11 +50,11 @@ public partial interface IConfigurationBuilder
     }
     public partial interface IConfigurationProvider
     {
-        System.Collections.Generic.IEnumerable<string> GetChildKeys(System.Collections.Generic.IEnumerable<string> earlierKeys, string parentPath);
+        System.Collections.Generic.IEnumerable<string> GetChildKeys(System.Collections.Generic.IEnumerable<string> earlierKeys, string? parentPath);
         Microsoft.Extensions.Primitives.IChangeToken GetReloadToken();
         void Load();
-        void Set(string key, string value);
-        bool TryGet(string key, out string value);
+        void Set(string key, string? value);
+        bool TryGet(string key, out string? value);
     }
     public partial interface IConfigurationRoot : Microsoft.Extensions.Configuration.IConfiguration
     {
@@ -64,7 +65,7 @@ public partial interface IConfigurationSection : Microsoft.Extensions.Configurat
     {
         string Key { get; }
         string Path { get; }
-        string Value { get; set; }
+        string? Value { get; set; }
     }
     public partial interface IConfigurationSource
     {
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.csproj
index f026a351a444f7114a2a2ba314e7bf516503c6a8..3e4c0cc8363b97692e1129d2b80ea60b49f5ea41 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/ref/Microsoft.Extensions.Configuration.Abstractions.csproj
@@ -1,6 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Include="Microsoft.Extensions.Configuration.Abstractions.cs" />
@@ -8,4 +9,8 @@
   <ItemGroup>
     <ProjectReference Include="$(LibrariesProjectRoot)Microsoft.Extensions.Primitives\ref\Microsoft.Extensions.Primitives.csproj" />
   </ItemGroup>
+  <ItemGroup Condition="'$(TargetFrameworkIdentifier)' == '.NETCoreApp'">
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Collections\ref\System.Collections.csproj" />
+    <ProjectReference Include="$(LibrariesProjectRoot)System.Runtime\ref\System.Runtime.csproj" />
+  </ItemGroup>
 </Project>
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationExtensions.cs b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationExtensions.cs
index 71cc406e34d17cb9345c9c7225a4caf256ed107f..07999be0e72bc93d453b933507a620eaec60d48f 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationExtensions.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 using System.Linq;
 
 namespace Microsoft.Extensions.Configuration
@@ -18,7 +19,7 @@ public static class ConfigurationExtensions
         /// <param name="builder">The builder to add to.</param>
         /// <param name="configureSource">Configures the source secrets.</param>
         /// <returns>The <see cref="IConfigurationBuilder"/>.</returns>
-        public static IConfigurationBuilder Add<TSource>(this IConfigurationBuilder builder, Action<TSource> configureSource) where TSource : IConfigurationSource, new()
+        public static IConfigurationBuilder Add<TSource>(this IConfigurationBuilder builder, Action<TSource>? configureSource) where TSource : IConfigurationSource, new()
         {
             var source = new TSource();
             configureSource?.Invoke(source);
@@ -31,9 +32,9 @@ public static IConfigurationBuilder Add<TSource>(this IConfigurationBuilder buil
         /// <param name="configuration">The configuration to enumerate.</param>
         /// <param name="name">The connection string key.</param>
         /// <returns>The connection string.</returns>
-        public static string GetConnectionString(this IConfiguration configuration, string name)
+        public static string? GetConnectionString(this IConfiguration configuration, string name)
         {
-            return configuration?.GetSection("ConnectionStrings")?[name];
+            return configuration?.GetSection("ConnectionStrings")[name];
         }
 
         /// <summary>
@@ -41,7 +42,7 @@ public static string GetConnectionString(this IConfiguration configuration, stri
         /// </summary>
         /// <param name="configuration">The configuration to enumerate.</param>
         /// <returns>An enumeration of key value pairs.</returns>
-        public static IEnumerable<KeyValuePair<string, string>> AsEnumerable(this IConfiguration configuration) => configuration.AsEnumerable(makePathsRelative: false);
+        public static IEnumerable<KeyValuePair<string, string?>> AsEnumerable(this IConfiguration configuration) => configuration.AsEnumerable(makePathsRelative: false);
 
         /// <summary>
         /// Get the enumeration of key value pairs within the <see cref="IConfiguration" />
@@ -49,19 +50,18 @@ public static string GetConnectionString(this IConfiguration configuration, stri
         /// <param name="configuration">The configuration to enumerate.</param>
         /// <param name="makePathsRelative">If true, the child keys returned will have the current configuration's Path trimmed from the front.</param>
         /// <returns>An enumeration of key value pairs.</returns>
-        public static IEnumerable<KeyValuePair<string, string>> AsEnumerable(this IConfiguration configuration, bool makePathsRelative)
+        public static IEnumerable<KeyValuePair<string, string?>> AsEnumerable(this IConfiguration configuration, bool makePathsRelative)
         {
             var stack = new Stack<IConfiguration>();
             stack.Push(configuration);
-            var rootSection = configuration as IConfigurationSection;
-            int prefixLength = (makePathsRelative && rootSection != null) ? rootSection.Path.Length + 1 : 0;
+            int prefixLength = (makePathsRelative && configuration is IConfigurationSection rootSection) ? rootSection.Path.Length + 1 : 0;
             while (stack.Count > 0)
             {
                 IConfiguration config = stack.Pop();
                 // Don't include the sections value if we are removing paths, since it will be an empty key
                 if (config is IConfigurationSection section && (!makePathsRelative || config != configuration))
                 {
-                    yield return new KeyValuePair<string, string>(section.Path.Substring(prefixLength), section.Value);
+                    yield return new KeyValuePair<string, string?>(section.Path.Substring(prefixLength), section.Value);
                 }
                 foreach (IConfigurationSection child in config.GetChildren())
                 {
@@ -75,7 +75,7 @@ public static string GetConnectionString(this IConfiguration configuration, stri
         /// </summary>
         /// <param name="section">The section to enumerate.</param>
         /// <returns><see langword="true" /> if the section has values or children; otherwise, <see langword="false" />.</returns>
-        public static bool Exists(this IConfigurationSection section)
+        public static bool Exists([NotNullWhen(true)] this IConfigurationSection? section)
         {
             if (section == null)
             {
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationPath.cs b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationPath.cs
index 2ad9e073d4f4e06f2a9da1e0c9b1d524e0d828ff..814d9113c840fa0a04234e1c65f8977dca5d5c77 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationPath.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationPath.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Microsoft.Extensions.Configuration
 {
@@ -49,7 +50,8 @@ public static string Combine(IEnumerable<string> pathSegments)
         /// </summary>
         /// <param name="path">The path.</param>
         /// <returns>The last path segment of the path.</returns>
-        public static string GetSectionKey(string path)
+        [return: NotNullIfNotNull("path")]
+        public static string? GetSectionKey(string? path)
         {
             if (string.IsNullOrEmpty(path))
             {
@@ -65,7 +67,7 @@ public static string GetSectionKey(string path)
         /// </summary>
         /// <param name="path">The path.</param>
         /// <returns>The original path minus the last individual segment found in it. Null if the original path corresponds to a top level node.</returns>
-        public static string GetParentPath(string path)
+        public static string? GetParentPath(string? path)
         {
             if (string.IsNullOrEmpty(path))
             {
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationRootExtensions.cs b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationRootExtensions.cs
index b6976a734cfa9ccbbf1450e12656bdc6110d6661..39abb8ec871e9f1b79d6e55bc6666823d31c8645 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationRootExtensions.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/ConfigurationRootExtensions.cs
@@ -25,7 +25,7 @@ public static string GetDebugView(this IConfigurationRoot root)
             {
                 foreach (IConfigurationSection child in children)
                 {
-                    (string Value, IConfigurationProvider Provider) valueAndProvider = GetValueAndProvider(root, child.Path);
+                    (string? Value, IConfigurationProvider? Provider) valueAndProvider = GetValueAndProvider(root, child.Path);
 
                     if (valueAndProvider.Provider != null)
                     {
@@ -57,13 +57,13 @@ public static string GetDebugView(this IConfigurationRoot root)
             return builder.ToString();
         }
 
-        private static (string Value, IConfigurationProvider Provider) GetValueAndProvider(
+        private static (string? Value, IConfigurationProvider? Provider) GetValueAndProvider(
             IConfigurationRoot root,
             string key)
         {
             foreach (IConfigurationProvider provider in root.Providers.Reverse())
             {
-                if (provider.TryGet(key, out string value))
+                if (provider.TryGet(key, out string? value))
                 {
                     return (value, provider);
                 }
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfiguration.cs b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfiguration.cs
index ce6b52b6601fa0fbc25f499e189861eecab2535a..0e9da61368546e862aa81b88a52ebc754986e069 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfiguration.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfiguration.cs
@@ -16,7 +16,7 @@ public interface IConfiguration
         /// </summary>
         /// <param name="key">The configuration key.</param>
         /// <returns>The configuration value.</returns>
-        string this[string key] { get; set; }
+        string? this[string key] { get; set; }
 
         /// <summary>
         /// Gets a configuration sub-section with the specified key.
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationProvider.cs
index 14d7940d41f02e68c5ee01ca649fdf446388447c..20a7e5a6694f80f539cc01fe9dc37d7ce99cddfa 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationProvider.cs
@@ -17,14 +17,14 @@ public interface IConfigurationProvider
         /// <param name="key">The key.</param>
         /// <param name="value">The value.</param>
         /// <returns><c>True</c> if a value for the specified key was found, otherwise <c>false</c>.</returns>
-        bool TryGet(string key, out string value);
+        bool TryGet(string key, out string? value);
 
         /// <summary>
         /// Sets a configuration value for the specified key.
         /// </summary>
         /// <param name="key">The key.</param>
         /// <param name="value">The value.</param>
-        void Set(string key, string value);
+        void Set(string key, string? value);
 
         /// <summary>
         /// Returns a change token if this provider supports change tracking, null otherwise.
@@ -45,6 +45,6 @@ public interface IConfigurationProvider
         /// <param name="earlierKeys">The child keys returned by the preceding providers for the same parent path.</param>
         /// <param name="parentPath">The parent path.</param>
         /// <returns>The child keys.</returns>
-        IEnumerable<string> GetChildKeys(IEnumerable<string> earlierKeys, string parentPath);
+        IEnumerable<string> GetChildKeys(IEnumerable<string> earlierKeys, string? parentPath);
     }
 }
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationSection.cs b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationSection.cs
index 4e47e7cca87b2e8343f6af7e431987e207146ec7..00047e94635702c82f3341b3d40978831ee8c3d2 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationSection.cs
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/IConfigurationSection.cs
@@ -21,6 +21,6 @@ public interface IConfigurationSection : IConfiguration
         /// <summary>
         /// Gets or sets the section value.
         /// </summary>
-        string Value { get; set; }
+        string? Value { get; set; }
     }
 }
diff --git a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj
index 0b79f05f830223dda3552e26067043dbdc41f96a..49aabd359e3fce1c059ccc441662ed7ebac545eb 100644
--- a/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj
+++ b/src/libraries/Microsoft.Extensions.Configuration.Abstractions/src/Microsoft.Extensions.Configuration.Abstractions.csproj
@@ -1,8 +1,11 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFrameworks>netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <TargetFrameworks>$(NetCoreAppCurrent);netstandard2.0;$(NetFrameworkMinimum)</TargetFrameworks>
+    <Nullable>enable</Nullable>
     <EnableDefaultItems>true</EnableDefaultItems>
+    <!-- Use targeting pack references instead of granular ones in the project file. -->
+    <DisableImplicitAssemblyReferences>false</DisableImplicitAssemblyReferences>
     <PackageDescription>Abstractions of key-value pair based configuration.
 
 Commonly Used Types:
diff --git a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/FakeConfigurationProvider.cs b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/FakeConfigurationProvider.cs
index 62f25a8d5862ae0350bc7eb5dc6d6ac850c5e463..0fe4747f666620b0e93c8664d29d06e4c72710f8 100644
--- a/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/FakeConfigurationProvider.cs
+++ b/src/libraries/Microsoft.Extensions.Options.ConfigurationExtensions/tests/FakeConfigurationProvider.cs
@@ -11,7 +11,7 @@ internal class FakeConfigurationProvider : MemoryConfigurationProvider, IConfigu
         public FakeConfigurationProvider(MemoryConfigurationSource source)
             : base(source) { }
 
-        public new void Set(string key, string value)
+        public new void Set(string key, string? value)
         {
             base.Set(key, value);
             OnReload();