diff --git a/src/Microsoft.AspNet.Identity/UserOptions.cs b/src/Microsoft.AspNet.Identity/UserOptions.cs
index 5b2578aa3b..214d7f9e1e 100644
--- a/src/Microsoft.AspNet.Identity/UserOptions.cs
+++ b/src/Microsoft.AspNet.Identity/UserOptions.cs
@@ -1,20 +1,18 @@
 // 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.Text.RegularExpressions;
+
 namespace Microsoft.AspNet.Identity
 {
     public class UserOptions
     {
         public UserOptions()
         {
-            AllowOnlyAlphanumericNames = true;
             //User.RequireUniqueEmail = true; // TODO: app decision?
         }
 
-        /// <summary>
-        ///     Only allow [A-Za-z0-9@_] in UserNames
-        /// </summary>
-        public bool AllowOnlyAlphanumericNames { get; set; }
+        public string UserNameValidationRegex { get; set; } = "^[a-zA-Z0-9@_\\.]+$";
 
         /// <summary>
         ///     If set, enforces that emails are non empty, valid, and unique
diff --git a/src/Microsoft.AspNet.Identity/UserValidator.cs b/src/Microsoft.AspNet.Identity/UserValidator.cs
index 2fea50531d..749f3a9f3f 100644
--- a/src/Microsoft.AspNet.Identity/UserValidator.cs
+++ b/src/Microsoft.AspNet.Identity/UserValidator.cs
@@ -4,10 +4,10 @@
 using System;
 using System.Collections.Generic;
 using System.Globalization;
-using System.Linq;
 #if ASPNET50
 using System.Net.Mail;
 #endif
+using System.Text.RegularExpressions;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -46,48 +46,6 @@ namespace Microsoft.AspNet.Identity
             return errors.Count > 0 ? IdentityResult.Failed(errors.ToArray()) : IdentityResult.Success;
         }
 
-        // TODO: Revisit extensibility for Validators
-
-        /// <summary>
-        ///     Returns true if the character is a digit between '0' and '9'
-        /// </summary>
-        /// <param name="c"></param>
-        /// <returns></returns>
-        public virtual bool IsDigit(char c)
-        {
-            return c >= '0' && c <= '9';
-        }
-
-        /// <summary>
-        ///     Returns true if the character is between 'a' and 'z'
-        /// </summary>
-        /// <param name="c"></param>
-        /// <returns></returns>
-        public virtual bool IsLower(char c)
-        {
-            return c >= 'a' && c <= 'z';
-        }
-
-        /// <summary>
-        ///     Returns true if the character is between 'A' and 'Z'
-        /// </summary>
-        /// <param name="c"></param>
-        /// <returns></returns>
-        public virtual bool IsUpper(char c)
-        {
-            return c >= 'A' && c <= 'Z';
-        }
-
-        /// <summary>
-        ///     Returns true if the character is upper, lower, a digit, or a common email character [@_.]
-        /// </summary>
-        /// <param name="c"></param>
-        /// <returns></returns>
-        public virtual bool IsAlphaNumeric(char c)
-        {
-            return IsUpper(c) || IsLower(c) || IsDigit(c) || c == '@' || c == '_' || c == '.';
-        }
-
         private async Task ValidateUserName(UserManager<TUser> manager, TUser user, ICollection<string> errors)
         {
             var userName = await manager.GetUserNameAsync(user);
@@ -95,9 +53,8 @@ namespace Microsoft.AspNet.Identity
             {
                 errors.Add(String.Format(CultureInfo.CurrentCulture, Resources.PropertyTooShort, "UserName"));
             }
-            else if (manager.Options.User.AllowOnlyAlphanumericNames && !userName.All(IsAlphaNumeric))
+            else if (manager.Options.User.UserNameValidationRegex != null && !Regex.IsMatch(userName, manager.Options.User.UserNameValidationRegex))
             {
-                // If any characters are not letters or digits, its an illegal user name
                 errors.Add(String.Format(CultureInfo.CurrentCulture, Resources.InvalidUserName, userName));
             }
             else
diff --git a/src/Microsoft.AspNet.Identity/project.json b/src/Microsoft.AspNet.Identity/project.json
index 6c44cd8eac..68b759996b 100644
--- a/src/Microsoft.AspNet.Identity/project.json
+++ b/src/Microsoft.AspNet.Identity/project.json
@@ -34,6 +34,7 @@
         "System.Security.Cryptography.Hashing.Algorithms": "4.0.0.0",
         "System.Text.Encoding": "4.0.10.0",
         "System.Text.Encoding.Extensions": "4.0.10.0",
+        "System.Text.RegularExpressions": "4.0.0.0",
         "System.Threading.Tasks": "4.0.10.0"
       }
     }
diff --git a/test/Microsoft.AspNet.Identity.InMemory.Test/InMemoryStoreTest.cs b/test/Microsoft.AspNet.Identity.InMemory.Test/InMemoryStoreTest.cs
index 3eb8ea1aa5..d72a7cc5ff 100644
--- a/test/Microsoft.AspNet.Identity.InMemory.Test/InMemoryStoreTest.cs
+++ b/test/Microsoft.AspNet.Identity.InMemory.Test/InMemoryStoreTest.cs
@@ -27,7 +27,7 @@ namespace Microsoft.AspNet.Identity.InMemory.Test
                 options.Password.RequireLowercase = false;
                 options.Password.RequireNonLetterOrDigit = false;
                 options.Password.RequireUppercase = false;
-                options.User.AllowOnlyAlphanumericNames = false;
+                options.User.UserNameValidationRegex = null;
             });
             return services.BuildServiceProvider().GetService<UserManager<IdentityUser>>();
         }
diff --git a/test/Microsoft.AspNet.Identity.SqlServer.InMemory.Test/InMemoryEFUserStoreTest.cs b/test/Microsoft.AspNet.Identity.SqlServer.InMemory.Test/InMemoryEFUserStoreTest.cs
index 70e3d9eaf6..ef93470e05 100644
--- a/test/Microsoft.AspNet.Identity.SqlServer.InMemory.Test/InMemoryEFUserStoreTest.cs
+++ b/test/Microsoft.AspNet.Identity.SqlServer.InMemory.Test/InMemoryEFUserStoreTest.cs
@@ -31,7 +31,7 @@ namespace Microsoft.AspNet.Identity.SqlServer.InMemory.Test
                 options.Password.RequireLowercase = false;
                 options.Password.RequireNonLetterOrDigit = false;
                 options.Password.RequireUppercase = false;
-                options.User.AllowOnlyAlphanumericNames = false;
+                options.User.UserNameValidationRegex = null;
             });
             return services.BuildServiceProvider().GetService<UserManager<IdentityUser>>();
         }
diff --git a/test/Microsoft.AspNet.Identity.SqlServer.Test/SqlStoreTestBase.cs b/test/Microsoft.AspNet.Identity.SqlServer.Test/SqlStoreTestBase.cs
index 050c37a069..cdab3b7037 100644
--- a/test/Microsoft.AspNet.Identity.SqlServer.Test/SqlStoreTestBase.cs
+++ b/test/Microsoft.AspNet.Identity.SqlServer.Test/SqlStoreTestBase.cs
@@ -146,7 +146,7 @@ namespace Microsoft.AspNet.Identity.SqlServer.Test
                     options.Password.RequireNonLetterOrDigit = false;
                     options.Password.RequireUppercase = false;
                     options.Password.RequireDigit = false;
-                    options.User.AllowOnlyAlphanumericNames = false;
+                    options.User.UserNameValidationRegex = null;
                 });
                 services.SetupOptions<DbContextOptions>(options =>
                     options.UseSqlServer(ConnectionString));
diff --git a/test/Microsoft.AspNet.Identity.Test/IdentityOptionsTest.cs b/test/Microsoft.AspNet.Identity.Test/IdentityOptionsTest.cs
index 960ed8fbac..3c6b9d66b2 100644
--- a/test/Microsoft.AspNet.Identity.Test/IdentityOptionsTest.cs
+++ b/test/Microsoft.AspNet.Identity.Test/IdentityOptionsTest.cs
@@ -29,7 +29,7 @@ namespace Microsoft.AspNet.Identity.Test
             Assert.True(options.Password.RequireUppercase);
             Assert.Equal(6, options.Password.RequiredLength);
 
-            Assert.True(options.User.AllowOnlyAlphanumericNames);
+            Assert.Equal("^[a-zA-Z0-9@_\\.]+$", options.User.UserNameValidationRegex);
             Assert.False(options.User.RequireUniqueEmail);
 
             Assert.Equal(ClaimTypes.Role, options.ClaimsIdentity.RoleClaimType);
@@ -77,8 +77,7 @@ namespace Microsoft.AspNet.Identity.Test
             Assert.Equal(usernameClaimType, options.ClaimsIdentity.UserNameClaimType);
             Assert.Equal(securityStampClaimType, options.ClaimsIdentity.SecurityStampClaimType);
             Assert.True(options.User.RequireUniqueEmail);
-            Assert.True(options.User.AllowOnlyAlphanumericNames);
-            Assert.True(options.User.AllowOnlyAlphanumericNames);
+            Assert.Equal("^[a-zA-Z0-9@_\\.]+$", options.User.UserNameValidationRegex);
             Assert.False(options.Password.RequireDigit);
             Assert.False(options.Password.RequireLowercase);
             Assert.False(options.Password.RequireNonLetterOrDigit);
diff --git a/test/Microsoft.AspNet.Identity.Test/UserValidatorTest.cs b/test/Microsoft.AspNet.Identity.Test/UserValidatorTest.cs
index a79b8bbf31..793dd36598 100644
--- a/test/Microsoft.AspNet.Identity.Test/UserValidatorTest.cs
+++ b/test/Microsoft.AspNet.Identity.Test/UserValidatorTest.cs
@@ -76,7 +76,7 @@ namespace Microsoft.AspNet.Identity.Test
         {
             // Setup
             var manager = MockHelpers.TestUserManager(new NoopUserStore());
-            manager.Options.User.AllowOnlyAlphanumericNames = false;
+            manager.Options.User.UserNameValidationRegex = null;
             var validator = new UserValidator<TestUser>();
             var user = new TestUser {UserName = userName};
 
diff --git a/test/Shared/MockHelpers.cs b/test/Shared/MockHelpers.cs
index c7b09dcc50..89825915c3 100644
--- a/test/Shared/MockHelpers.cs
+++ b/test/Shared/MockHelpers.cs
@@ -24,7 +24,7 @@ namespace Microsoft.AspNet.Identity.Test
                 options.Password.RequireLowercase = false;
                 options.Password.RequireNonLetterOrDigit = false;
                 options.Password.RequireUppercase = false;
-                options.User.AllowOnlyAlphanumericNames = false;
+                options.User.UserNameValidationRegex = null;
             });
             return services.BuildServiceProvider().GetService<UserManager<TUser>>();
         }
diff --git a/test/Shared/UserManagerTestBase.cs b/test/Shared/UserManagerTestBase.cs
index ab2b45a68e..44e34c0eeb 100644
--- a/test/Shared/UserManagerTestBase.cs
+++ b/test/Shared/UserManagerTestBase.cs
@@ -392,7 +392,7 @@ namespace Microsoft.AspNet.Identity.Test
         {
             var manager = CreateManager();
             manager.Options.User.UseUserNameAsEmail = true;
-            manager.Options.User.AllowOnlyAlphanumericNames = false;
+            manager.Options.User.UserNameValidationRegex = null;
             var user = CreateTestUser();
             var email = user.UserName + "@test.com";
             user.UserName = email;