diff --git a/Octokit.Tests/Octokit.Tests.csproj b/Octokit.Tests/Octokit.Tests.csproj
index af4759db..1b1e35de 100644
--- a/Octokit.Tests/Octokit.Tests.csproj
+++ b/Octokit.Tests/Octokit.Tests.csproj
@@ -104,6 +104,7 @@
     <Compile Include="Helpers\StringExtensionsTests.cs" />
     <Compile Include="Clients\RepositoriesClientTests.cs" />
     <Compile Include="Reactive\AuthorizationExtensionsTests.cs" />
+    <Compile Include="Reactive\ObservableMilestonesClientTests.cs" />
     <Compile Include="Reactive\ObservableRepositoriesClientTests.cs" />
     <Compile Include="SimpleJsonSerializerTests.cs" />
     <Compile Include="Clients\UsersClientTests.cs" />
diff --git a/Octokit.Tests/Reactive/ObservableMilestonesClientTests.cs b/Octokit.Tests/Reactive/ObservableMilestonesClientTests.cs
new file mode 100644
index 00000000..baa18f30
--- /dev/null
+++ b/Octokit.Tests/Reactive/ObservableMilestonesClientTests.cs
@@ -0,0 +1,264 @@
+using System;
+using System.Collections.Generic;
+using System.Reactive.Linq;
+using System.Threading.Tasks;
+using NSubstitute;
+using Octokit;
+using Octokit.Internal;
+using Octokit.Reactive.Clients;
+using Octokit.Tests.Helpers;
+using Xunit;
+
+namespace Octokit.Tests.Reactive
+{
+    public class ObservableMilestonesClientTests
+    {
+        public class TheGetMethod
+        {
+            [Fact]
+            public void GetsFromClientIssueMilestone()
+            {
+                var gitHubClient = Substitute.For<IGitHubClient>();
+                var client = new ObservableMilestonesClient(gitHubClient);
+
+                client.Get("fake", "repo", 42);
+
+                gitHubClient.Issue.Milestone.Received().Get("fake", "repo", 42);
+            }
+
+            [Fact]
+            public async Task EnsuresNonNullArguments()
+            {
+                var client = new ObservableMilestonesClient(Substitute.For<IGitHubClient>());
+
+                await AssertEx.Throws<ArgumentNullException>(async () => await client.Get(null, "name", 1));
+                await AssertEx.Throws<ArgumentNullException>(async () => await client.Get("owner", null, 1));
+                await AssertEx.Throws<ArgumentException>(async () => await client.Get(null, "", 1));
+                await AssertEx.Throws<ArgumentException>(async () => await client.Get("", null, 1));
+            }
+        }
+
+        public class TheGetForRepositoryMethod
+        {
+            [Fact]
+            public void ReturnsEveryPageOfMilestones()
+            {
+                var firstPageUrl = new Uri("repos/fake/repo/milestones", UriKind.Relative);
+                var secondPageUrl = new Uri("https://example.com/page/2");
+                var firstPageLinks = new Dictionary<string, Uri> {{"next", secondPageUrl}};
+                var firstPageResponse = new ApiResponse<List<Milestone>>
+                {
+                    BodyAsObject = new List<Milestone>
+                    {
+                        new Milestone {Number = 1},
+                        new Milestone {Number = 2},
+                        new Milestone {Number = 3},
+                    },
+                    ApiInfo = CreateApiInfo(firstPageLinks)
+                };
+                var thirdPageUrl = new Uri("https://example.com/page/3");
+                var secondPageLinks = new Dictionary<string, Uri> {{"next", thirdPageUrl}};
+                var secondPageResponse = new ApiResponse<List<Milestone>>
+                {
+                    BodyAsObject = new List<Milestone>
+                    {
+                        new Milestone {Number = 4},
+                        new Milestone {Number = 5},
+                        new Milestone {Number = 6},
+                    },
+                    ApiInfo = CreateApiInfo(secondPageLinks)
+                };
+                var lastPageResponse = new ApiResponse<List<Milestone>>
+                {
+                    BodyAsObject = new List<Milestone>
+                    {
+                        new Milestone {Number = 7},
+                    },
+                    ApiInfo = CreateApiInfo(new Dictionary<string, Uri>())
+                };
+                var gitHubClient = Substitute.For<IGitHubClient>();
+                gitHubClient.Connection.GetAsync<List<Milestone>>(firstPageUrl, null, null)
+                    .Returns(Task.Factory.StartNew<IResponse<List<Milestone>>>(() => firstPageResponse));
+                gitHubClient.Connection.GetAsync<List<Milestone>>(secondPageUrl, null, null)
+                    .Returns(Task.Factory.StartNew<IResponse<List<Milestone>>>(() => secondPageResponse));
+                gitHubClient.Connection.GetAsync<List<Milestone>>(thirdPageUrl, null, null)
+                    .Returns(Task.Factory.StartNew<IResponse<List<Milestone>>>(() => lastPageResponse));
+                var client = new ObservableMilestonesClient(gitHubClient);
+
+                var results = client.GetForRepository("fake", "repo").ToArray().Wait();
+
+                Assert.Equal(7, results.Length);
+                Assert.Equal(firstPageResponse.BodyAsObject[0].Number, results[0].Number);
+                Assert.Equal(secondPageResponse.BodyAsObject[1].Number, results[4].Number);
+                Assert.Equal(lastPageResponse.BodyAsObject[0].Number, results[6].Number);
+            }
+
+            [Fact]
+            public void SendsAppropriateParameters()
+            {
+                var firstPageUrl = new Uri("repos/fake/repo/milestones", UriKind.Relative);
+                var secondPageUrl = new Uri("https://example.com/page/2");
+                var firstPageLinks = new Dictionary<string, Uri> {{"next", secondPageUrl}};
+                var firstPageResponse = new ApiResponse<List<Milestone>>
+                {
+                    BodyAsObject = new List<Milestone>
+                    {
+                        new Milestone {Number = 1},
+                        new Milestone {Number = 2},
+                        new Milestone {Number = 3},
+                    },
+                    ApiInfo = CreateApiInfo(firstPageLinks)
+                };
+                var thirdPageUrl = new Uri("https://example.com/page/3");
+                var secondPageLinks = new Dictionary<string, Uri> {{"next", thirdPageUrl}};
+                var secondPageResponse = new ApiResponse<List<Milestone>>
+                {
+                    BodyAsObject = new List<Milestone>
+                    {
+                        new Milestone {Number = 4},
+                        new Milestone {Number = 5},
+                        new Milestone {Number = 6},
+                    },
+                    ApiInfo = CreateApiInfo(secondPageLinks)
+                };
+                var lastPageResponse = new ApiResponse<List<Milestone>>
+                {
+                    BodyAsObject = new List<Milestone>
+                    {
+                        new Milestone {Number = 7},
+                    },
+                    ApiInfo = CreateApiInfo(new Dictionary<string, Uri>())
+                };
+                var gitHubClient = Substitute.For<IGitHubClient>();
+                gitHubClient.Connection.GetAsync<List<Milestone>>(Arg.Is(firstPageUrl),
+                    Arg.Is<Dictionary<string, string>>(d => d.Count == 3
+                        && d["direction"] == "desc"
+                        && d["state"] == "open"
+                        && d["sort"] == "due_date"), Arg.Any<string>())
+                    .Returns(Task.Factory.StartNew<IResponse<List<Milestone>>>(() => firstPageResponse));
+                gitHubClient.Connection.GetAsync<List<Milestone>>(secondPageUrl, null, null)
+                    .Returns(Task.Factory.StartNew<IResponse<List<Milestone>>>(() => secondPageResponse));
+                gitHubClient.Connection.GetAsync<List<Milestone>>(thirdPageUrl, null, null)
+                    .Returns(Task.Factory.StartNew<IResponse<List<Milestone>>>(() => lastPageResponse));
+                var client = new ObservableMilestonesClient(gitHubClient);
+
+                var results = client.GetForRepository("fake", "repo", new MilestoneRequest { SortDirection = SortDirection.Descending }).ToArray().Wait();
+
+                Assert.Equal(7, results.Length);
+                Assert.Equal(firstPageResponse.BodyAsObject[0].Number, results[0].Number);
+                Assert.Equal(secondPageResponse.BodyAsObject[1].Number, results[4].Number);
+                Assert.Equal(lastPageResponse.BodyAsObject[0].Number, results[6].Number);
+            }
+        }
+
+        public class TheCreateMethod
+        {
+            [Fact]
+            public void CreatesFromClientIssueMilestone()
+            {
+                var newMilestone = new NewMilestone("some title");
+                var gitHubClient = Substitute.For<IGitHubClient>();
+                var client = new ObservableMilestonesClient(gitHubClient);
+
+                client.Create("fake", "repo", newMilestone);
+
+                gitHubClient.Issue.Milestone.Received().Create("fake", "repo", newMilestone);
+            }
+
+            [Fact]
+            public async Task EnsuresArgumentsNotNull()
+            {
+                var gitHubClient = Substitute.For<IGitHubClient>();
+                var client = new ObservableMilestonesClient(gitHubClient);
+
+                AssertEx.Throws<ArgumentNullException>(async () => await
+                    client.Create(null, "name", new NewMilestone("title")));
+                AssertEx.Throws<ArgumentException>(async () => await
+                    client.Create("", "name", new NewMilestone("x")));
+                AssertEx.Throws<ArgumentNullException>(async () => await
+                    client.Create("owner", null, new NewMilestone("x")));
+                AssertEx.Throws<ArgumentException>(async () => await
+                    client.Create("owner", "", new NewMilestone("x")));
+                AssertEx.Throws<ArgumentNullException>(async () => await
+                    client.Create("owner", "name", null));
+            }
+        }
+
+        public class TheUpdateMethod
+        {
+            [Fact]
+            public void UpdatesClientIssueMilestone()
+            {
+                var milestoneUpdate = new MilestoneUpdate();
+                var gitHubClient = Substitute.For<IGitHubClient>();
+                var client = new ObservableMilestonesClient(gitHubClient);
+
+                client.Update("fake", "repo", 42, milestoneUpdate);
+
+                gitHubClient.Issue.Milestone.Received().Update("fake", "repo", 42, milestoneUpdate);
+            }
+
+            [Fact]
+            public async Task EnsuresArgumentsNotNull()
+            {
+                var gitHubClient = Substitute.For<IGitHubClient>();
+                var client = new ObservableMilestonesClient(gitHubClient);
+
+                AssertEx.Throws<ArgumentNullException>(async () => await
+                    client.Create(null, "name", new NewMilestone("title")));
+                AssertEx.Throws<ArgumentException>(async () => await
+                    client.Create("", "name", new NewMilestone("x")));
+                AssertEx.Throws<ArgumentNullException>(async () => await
+                    client.Create("owner", null, new NewMilestone("x")));
+                AssertEx.Throws<ArgumentException>(async () => await
+                    client.Create("owner", "", new NewMilestone("x")));
+                AssertEx.Throws<ArgumentNullException>(async () => await
+                    client.Create("owner", "name", null));
+            }
+        }
+
+        public class TheDeleteMethod
+        {
+            [Fact]
+            public void DeletesFromClientIssueMilestone()
+            {
+                var gitHubClient = Substitute.For<IGitHubClient>();
+                var client = new ObservableMilestonesClient(gitHubClient);
+
+                client.Delete("fake", "repo", 42);
+
+                gitHubClient.Issue.Milestone.Received().Delete("fake", "repo", 42);
+            }
+
+            [Fact]
+            public async Task EnsuresArgumentsNotNull()
+            {
+                var gitHubClient = Substitute.For<IGitHubClient>();
+                var client = new ObservableMilestonesClient(gitHubClient);
+
+                AssertEx.Throws<ArgumentNullException>(async () => await
+                    client.Delete(null, "name", 42));
+                AssertEx.Throws<ArgumentException>(async () => await
+                    client.Delete("", "name", 42));
+                AssertEx.Throws<ArgumentNullException>(async () => await
+                    client.Delete("owner", null, 42));
+                AssertEx.Throws<ArgumentException>(async () => await
+                    client.Delete("owner", "", 42));
+            }
+        }
+
+        public class TheCtor
+        {
+            [Fact]
+            public void EnsuresArgument()
+            {
+                Assert.Throws<ArgumentNullException>(() => new MilestonesClient(null));
+            }
+        }
+
+        static ApiInfo CreateApiInfo(IDictionary<string, Uri> links)
+        {
+            return new ApiInfo(links, new List<string>(), new List<string>(), "etag", new RateLimit(new Dictionary<string, string>()));
+        }
+    }
+}