diff --git a/build/dependencies.props b/build/dependencies.props
index 8b795c771b..620c2bd49d 100644
--- a/build/dependencies.props
+++ b/build/dependencies.props
@@ -14,6 +14,7 @@
     <MicrosoftAspNetCoreTestHostPackageVersion>2.1.0-preview3-32110</MicrosoftAspNetCoreTestHostPackageVersion>
     <MicrosoftExtensionsConfigurationAbstractionsPackageVersion>2.1.0-preview3-32110</MicrosoftExtensionsConfigurationAbstractionsPackageVersion>
     <MicrosoftExtensionsConfigurationBinderPackageVersion>2.1.0-preview3-32110</MicrosoftExtensionsConfigurationBinderPackageVersion>
+    <MicrosoftExtensionsConfigurationExtensionsPackageVersion>2.1.0-preview3-32110</MicrosoftExtensionsConfigurationExtensionsPackageVersion>
     <MicrosoftExtensionsConfigurationJsonPackageVersion>2.1.0-preview3-32110</MicrosoftExtensionsConfigurationJsonPackageVersion>
     <MicrosoftExtensionsFileProvidersAbstractionsPackageVersion>2.1.0-preview3-32110</MicrosoftExtensionsFileProvidersAbstractionsPackageVersion>
     <MicrosoftExtensionsLoggingAbstractionsPackageVersion>2.1.0-preview3-32110</MicrosoftExtensionsLoggingAbstractionsPackageVersion>
diff --git a/samples/HostFilteringSample/Program.cs b/samples/HostFilteringSample/Program.cs
index 0d4ffa9324..0ccc7cdb2e 100644
--- a/samples/HostFilteringSample/Program.cs
+++ b/samples/HostFilteringSample/Program.cs
@@ -25,8 +25,8 @@ namespace HostFilteringSample
                 .ConfigureAppConfiguration((hostingContext, config) =>
                 {
                     var env = hostingContext.HostingEnvironment;
-                    config.AddJsonFile("appsettings.json", optional: true)
-                          .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true);
+                    config.AddJsonFile("appsettings.json", optional: true, reloadOnChange: true)
+                          .AddJsonFile($"appsettings.{env.EnvironmentName}.json", optional: true, reloadOnChange: true);
                 })
                 .UseKestrel()
                 .UseStartup<Startup>();
diff --git a/samples/HostFilteringSample/Startup.cs b/samples/HostFilteringSample/Startup.cs
index 93c217b71c..283d8ee7f9 100644
--- a/samples/HostFilteringSample/Startup.cs
+++ b/samples/HostFilteringSample/Startup.cs
@@ -1,12 +1,15 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Builder;
+using Microsoft.AspNetCore.HostFiltering;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
 
 namespace HostFilteringSample
 {
@@ -23,9 +26,22 @@ namespace HostFilteringSample
         {
             services.AddHostFiltering(options =>
             {
-                // If this is excluded then it will fall back to the server's addresses
-                options.AllowedHosts = Config.GetSection("AllowedHosts").Get<List<string>>();
+
             });
+
+            // Fallback
+            services.PostConfigure<HostFilteringOptions>(options =>
+            {
+                if (options.AllowedHosts == null || options.AllowedHosts.Count == 0)
+                {
+                    // "AllowedHosts": "localhost;127.0.0.1;[::1]"
+                    var hosts = Config["AllowedHosts"]?.Split(new[] { ';' }, StringSplitOptions.RemoveEmptyEntries);
+                    // Fall back to "*" to disable.
+                    options.AllowedHosts = (hosts?.Length > 0 ? hosts : new[] { "*" });
+                }
+            });
+            // Change notification
+            services.AddSingleton<IOptionsChangeTokenSource<HostFilteringOptions>>(new ConfigurationChangeTokenSource<HostFilteringOptions>(Config));
         }
 
         public void Configure(IApplicationBuilder app, IHostingEnvironment env)
diff --git a/samples/HostFilteringSample/appsettings.Development.json b/samples/HostFilteringSample/appsettings.Development.json
index 7c2d8e26dc..b8d74ac7a2 100644
--- a/samples/HostFilteringSample/appsettings.Development.json
+++ b/samples/HostFilteringSample/appsettings.Development.json
@@ -1,3 +1,3 @@
 {
-  "AllowedHosts": [ "localhost", "127.0.0.1", "[::1]" ]
+  "AllowedHosts": "localhost;127.0.0.1;[::1]"
 }
diff --git a/samples/HostFilteringSample/appsettings.Production.json b/samples/HostFilteringSample/appsettings.Production.json
index f2fc90c390..0c6fabda95 100644
--- a/samples/HostFilteringSample/appsettings.Production.json
+++ b/samples/HostFilteringSample/appsettings.Production.json
@@ -1,3 +1,3 @@
 {
-  "AllowedHosts": [ "example.com", "localhost" ]
+  "AllowedHosts": "example.com;localhost"
 }
diff --git a/src/Microsoft.AspNetCore.HostFiltering/HostFilteringMiddleware.cs b/src/Microsoft.AspNetCore.HostFiltering/HostFilteringMiddleware.cs
index e1e38eca37..d355edd0fc 100644
--- a/src/Microsoft.AspNetCore.HostFiltering/HostFilteringMiddleware.cs
+++ b/src/Microsoft.AspNetCore.HostFiltering/HostFilteringMiddleware.cs
@@ -30,7 +30,8 @@ namespace Microsoft.AspNetCore.HostFiltering
 
         private readonly RequestDelegate _next;
         private readonly ILogger<HostFilteringMiddleware> _logger;
-        private readonly HostFilteringOptions _options;
+        private readonly IOptionsMonitor<HostFilteringOptions> _optionsMonitor;
+        private HostFilteringOptions _options;
         private IList<StringSegment> _allowedHosts;
         private bool? _allowAnyNonEmptyHost;
 
@@ -39,13 +40,21 @@ namespace Microsoft.AspNetCore.HostFiltering
         /// </summary>
         /// <param name="next"></param>
         /// <param name="logger"></param>
-        /// <param name="options"></param>
+        /// <param name="optionsMonitor"></param>
         public HostFilteringMiddleware(RequestDelegate next, ILogger<HostFilteringMiddleware> logger, 
-            IOptions<HostFilteringOptions> options)
+            IOptionsMonitor<HostFilteringOptions> optionsMonitor)
         {
             _next = next ?? throw new ArgumentNullException(nameof(next));
             _logger = logger ?? throw new ArgumentNullException(nameof(logger));
-            _options = options?.Value ?? throw new ArgumentNullException(nameof(options));
+            _optionsMonitor = optionsMonitor ?? throw new ArgumentNullException(nameof(optionsMonitor));
+            _options = _optionsMonitor.CurrentValue;
+            _optionsMonitor.OnChange(options =>
+            {
+                // Clear the cached settings so the next EnsureConfigured will re-evaluate.
+                _options = options;
+                _allowedHosts = new List<StringSegment>();
+                _allowAnyNonEmptyHost = null;
+            });
         }
 
         /// <summary>
@@ -55,9 +64,9 @@ namespace Microsoft.AspNetCore.HostFiltering
         /// <returns></returns>
         public Task Invoke(HttpContext context)
         {
-            EnsureConfigured();
+            var allowedHosts = EnsureConfigured();
 
-            if (!CheckHost(context))
+            if (!CheckHost(context, allowedHosts))
             {
                 context.Response.StatusCode = 400;
                 if (_options.IncludeFailureMessage)
@@ -72,19 +81,20 @@ namespace Microsoft.AspNetCore.HostFiltering
             return _next(context);
         }
 
-        private void EnsureConfigured()
+        private IList<StringSegment> EnsureConfigured()
         {
             if (_allowAnyNonEmptyHost == true || _allowedHosts?.Count > 0)
             {
-                return;
+                return _allowedHosts;
             }
 
             var allowedHosts = new List<StringSegment>();
             if (_options.AllowedHosts?.Count > 0 && !TryProcessHosts(_options.AllowedHosts, allowedHosts))
             {
                 _logger.LogDebug("Wildcard detected, all requests with hosts will be allowed.");
+                _allowedHosts = allowedHosts;
                 _allowAnyNonEmptyHost = true;
-                return;
+                return _allowedHosts;
             }
 
             if (allowedHosts.Count == 0)
@@ -94,6 +104,7 @@ namespace Microsoft.AspNetCore.HostFiltering
 
             _logger.LogDebug("Allowed hosts: " + string.Join("; ", allowedHosts));
             _allowedHosts = allowedHosts;
+            return _allowedHosts;
         }
 
         // returns false if any wildcards were found
@@ -127,7 +138,7 @@ namespace Microsoft.AspNetCore.HostFiltering
         }
 
         // This does not duplicate format validations that are expected to be performed by the host.
-        private bool CheckHost(HttpContext context)
+        private bool CheckHost(HttpContext context, IList<StringSegment> allowedHosts)
         {
             var host = new StringSegment(context.Request.Headers[HeaderNames.Host].ToString()).Trim();
 
@@ -153,7 +164,7 @@ namespace Microsoft.AspNetCore.HostFiltering
                 return true;
             }
 
-            if (HostString.MatchesAny(host, _allowedHosts))
+            if (HostString.MatchesAny(host, allowedHosts))
             {
                 _logger.LogTrace($"The host '{host}' matches an allowed host.");
                 return true;
diff --git a/test/Microsoft.AspNetCore.HostFiltering.Tests/HostFilteringMiddlewareTests.cs b/test/Microsoft.AspNetCore.HostFiltering.Tests/HostFilteringMiddlewareTests.cs
index 2fc7b8c713..ab45bc9554 100644
--- a/test/Microsoft.AspNetCore.HostFiltering.Tests/HostFilteringMiddlewareTests.cs
+++ b/test/Microsoft.AspNetCore.HostFiltering.Tests/HostFilteringMiddlewareTests.cs
@@ -2,10 +2,14 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Collections.Generic;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Builder;
 using Microsoft.AspNetCore.Hosting;
 using Microsoft.AspNetCore.TestHost;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Options;
 using Microsoft.Extensions.Primitives;
 using Microsoft.Net.Http.Headers;
 using Xunit;
@@ -179,5 +183,58 @@ namespace Microsoft.AspNetCore.HostFiltering
             var response = await server.CreateRequest("/").GetAsync();
             Assert.Equal(400, (int)response.StatusCode);
         }
+
+        [Fact]
+        public async Task SupportsDynamicOptionsReload()
+        {
+            var config = new ConfigurationBuilder().Add(new ReloadableMemorySource()).Build();
+            config["AllowedHosts"] = "localhost";
+            var currentHost = "otherHost";
+
+            var builder = new WebHostBuilder()
+                .ConfigureServices(services =>
+                {
+                    services.AddHostFiltering(options =>
+                    {
+                        options.AllowedHosts = new[] { config["AllowedHosts"] };
+                    });
+                    services.AddSingleton<IOptionsChangeTokenSource<HostFilteringOptions>>(new ConfigurationChangeTokenSource<HostFilteringOptions>(config));
+                })
+                .Configure(app =>
+                {
+                    app.Use((ctx, next) =>
+                    {
+                        ctx.Request.Headers[HeaderNames.Host] = currentHost;
+                        return next();
+                    });
+                    app.UseHostFiltering();
+                    app.Run(c => Task.CompletedTask);
+                });
+            var server = new TestServer(builder);
+            var response = await server.CreateRequest("/").GetAsync();
+            Assert.Equal(400, (int)response.StatusCode);
+
+            config["AllowedHosts"] = "otherHost";
+
+            response = await server.CreateRequest("/").GetAsync();
+            Assert.Equal(200, (int)response.StatusCode);
+        }
+
+        private class ReloadableMemorySource : IConfigurationSource
+        {
+            public IConfigurationProvider Build(IConfigurationBuilder builder)
+            {
+                return new ReloadableMemoryProvider();
+            }
+        }
+
+        internal class ReloadableMemoryProvider : ConfigurationProvider
+        {
+            public override void Set(string key, string value)
+            {
+                base.Set(key, value);
+                OnReload();
+            }
+        }
     }
 }
diff --git a/test/Microsoft.AspNetCore.HostFiltering.Tests/Microsoft.AspNetCore.HostFiltering.Tests.csproj b/test/Microsoft.AspNetCore.HostFiltering.Tests/Microsoft.AspNetCore.HostFiltering.Tests.csproj
index d71805c949..94262065fa 100644
--- a/test/Microsoft.AspNetCore.HostFiltering.Tests/Microsoft.AspNetCore.HostFiltering.Tests.csproj
+++ b/test/Microsoft.AspNetCore.HostFiltering.Tests/Microsoft.AspNetCore.HostFiltering.Tests.csproj
@@ -6,6 +6,7 @@
 
   <ItemGroup>
     <ProjectReference Include="..\..\src\Microsoft.AspNetCore.HostFiltering\Microsoft.AspNetCore.HostFiltering.csproj" />
+    <PackageReference Include="Microsoft.Extensions.Options.ConfigurationExtensions" Version="$(MicrosoftExtensionsConfigurationExtensionsPackageVersion)" />
   </ItemGroup>
 
 </Project>