diff --git a/src/Microsoft.Identity.Web.TokenAcquisition/DefaultTokenAcquirerFactoryImplementation.cs b/src/Microsoft.Identity.Web.TokenAcquisition/DefaultTokenAcquirerFactoryImplementation.cs
index 35c870d09..c4c76af60 100644
--- a/src/Microsoft.Identity.Web.TokenAcquisition/DefaultTokenAcquirerFactoryImplementation.cs
+++ b/src/Microsoft.Identity.Web.TokenAcquisition/DefaultTokenAcquirerFactoryImplementation.cs
@@ -2,9 +2,9 @@
 // Licensed under the MIT License.
 
 using System;
+using System.Collections.Concurrent;
 using System.Collections.Generic;
 using Microsoft.Extensions.DependencyInjection;
-using Microsoft.Extensions.Options;
 using Microsoft.Identity.Abstractions;
 
 namespace Microsoft.Identity.Web
@@ -17,7 +17,7 @@ public DefaultTokenAcquirerFactoryImplementation(IServiceProvider serviceProvide
         }
         private IServiceProvider ServiceProvider { get; set; }
 
-        readonly Dictionary<string, ITokenAcquirer> _authSchemes = new Dictionary<string, ITokenAcquirer>();
+        readonly ConcurrentDictionary<string, ITokenAcquirer> _authSchemes = new();
 
         /// <inheritdoc/>
         public ITokenAcquirer GetTokenAcquirer(
@@ -26,31 +26,31 @@ public ITokenAcquirer GetTokenAcquirer(
             IEnumerable<CredentialDescription> clientCredentials,
             string? region = null)
         {
-            CheckServiceProviderNotNull();
+            string key = GetKey(authority, clientId, region);
 
-            ITokenAcquirer? tokenAcquirer;
-            // Compute the key
-            string key = GetKey(authority, clientId);
-            if (!_authSchemes.TryGetValue(key, out tokenAcquirer))
-            {
-                MicrosoftIdentityApplicationOptions MicrosoftIdentityApplicationOptions = new MicrosoftIdentityApplicationOptions
-                {
-                    ClientId = clientId,
-                    Authority = authority,
-                    ClientCredentials = clientCredentials,
-                    SendX5C = true
-                };
-                if (region != null)
+            // GetOrAdd ONLY synchronizes the outcome. So, the factory might still be invoked multiple times.
+            // Therefore, all side-effects within this block must remain idempotent.
+            return _authSchemes.GetOrAdd(key, (key) =>
                 {
-                    MicrosoftIdentityApplicationOptions.AzureRegion = region;
-                }
+                    MicrosoftIdentityApplicationOptions MicrosoftIdentityApplicationOptions = new()
+                    {
+                        ClientId = clientId,
+                        Authority = authority,
+                        ClientCredentials = clientCredentials,
+                        SendX5C = true
+                    };
 
-                var optionsMonitor = ServiceProvider.GetRequiredService<IMergedOptionsStore>();
-                var mergedOptions = optionsMonitor.Get(key);
-                MergedOptions.UpdateMergedOptionsFromMicrosoftIdentityApplicationOptions(MicrosoftIdentityApplicationOptions, mergedOptions);
-                tokenAcquirer = GetTokenAcquirer(key);
-            }
-            return tokenAcquirer;
+                    if (region != null)
+                    {
+                        MicrosoftIdentityApplicationOptions.AzureRegion = region;
+                    }
+
+                    IMergedOptionsStore optionsMonitor = ServiceProvider.GetRequiredService<IMergedOptionsStore>();
+                    MergedOptions mergedOptions = optionsMonitor.Get(key);
+                    MergedOptions.UpdateMergedOptionsFromMicrosoftIdentityApplicationOptions(MicrosoftIdentityApplicationOptions, mergedOptions);
+
+                    return MakeTokenAcquirer(key);
+                });
         }
 
         /// <inheritdoc/>
@@ -58,8 +58,6 @@ public ITokenAcquirer GetTokenAcquirer(IdentityApplicationOptions IdentityApplic
         {
             _ = Throws.IfNull(IdentityApplicationOptions);
 
-            CheckServiceProviderNotNull();
-
             // Compute the Azure region if the option is a MicrosoftIdentityApplicationOptions.
             MicrosoftIdentityApplicationOptions? MicrosoftIdentityApplicationOptions = IdentityApplicationOptions as MicrosoftIdentityApplicationOptions;
             if (MicrosoftIdentityApplicationOptions == null)
@@ -77,33 +75,36 @@ public ITokenAcquirer GetTokenAcquirer(IdentityApplicationOptions IdentityApplic
                 };
             }
 
-            // Compute the key
-            ITokenAcquirer? tokenAcquirer;
-            string key = GetKey(IdentityApplicationOptions.Authority, IdentityApplicationOptions.ClientId);
-            if (!_authSchemes.TryGetValue(key, out tokenAcquirer))
+            string key = GetKey(IdentityApplicationOptions.Authority, IdentityApplicationOptions.ClientId, MicrosoftIdentityApplicationOptions.AzureRegion);
+
+            return _authSchemes.GetOrAdd(key, (key) =>
             {
-                var optionsMonitor = ServiceProvider!.GetRequiredService<IMergedOptionsStore>();
-                var mergedOptions = optionsMonitor.Get(key);
+                IMergedOptionsStore optionsMonitor = ServiceProvider!.GetRequiredService<IMergedOptionsStore>();
+                MergedOptions mergedOptions = optionsMonitor.Get(key);
+
+       
                 MergedOptions.UpdateMergedOptionsFromMicrosoftIdentityApplicationOptions(MicrosoftIdentityApplicationOptions, mergedOptions);
-                tokenAcquirer = GetTokenAcquirer(key);
-            }
-            return tokenAcquirer;
+                return MakeTokenAcquirer(key);
+            });
         }
 
         /// <inheritdoc/>
         public ITokenAcquirer GetTokenAcquirer(string authenticationScheme = "")
+        {
+            return _authSchemes.GetOrAdd(authenticationScheme, (key) =>
+            {
+                return MakeTokenAcquirer(authenticationScheme);
+            });
+        }
+
+        private ITokenAcquirer MakeTokenAcquirer(string authenticationScheme = "")
         {
             CheckServiceProviderNotNull();
 
-            ITokenAcquirer? acquirer;
-            if (!_authSchemes.TryGetValue(authenticationScheme, out acquirer))
-            {
-                var tokenAcquisition = ServiceProvider!.GetRequiredService<ITokenAcquisition>();
-                acquirer = new TokenAcquirer(tokenAcquisition, authenticationScheme);
-                _authSchemes.Add(authenticationScheme, acquirer);
-            }
-            return acquirer;
+            ITokenAcquisition tokenAcquisition = ServiceProvider!.GetRequiredService<ITokenAcquisition>();
+            return new TokenAcquirer(tokenAcquisition, authenticationScheme);
         }
+
         private void CheckServiceProviderNotNull()
         {
             if (ServiceProvider == null)
@@ -112,10 +113,9 @@ private void CheckServiceProviderNotNull()
             }
         }
 
-
-        private static string GetKey(string? authority, string? clientId)
+        public static string GetKey(string? authority, string? clientId, string? region)
         {
-            return $"{authority}{clientId}";
+            return $"{authority}{clientId}{region}";
         }
     }
 }
diff --git a/tests/E2E Tests/TokenAcquirerTests/TokenAcquirer.cs b/tests/E2E Tests/TokenAcquirerTests/TokenAcquirer.cs
index 15f66e00e..e10c2d805 100644
--- a/tests/E2E Tests/TokenAcquirerTests/TokenAcquirer.cs	
+++ b/tests/E2E Tests/TokenAcquirerTests/TokenAcquirer.cs	
@@ -2,10 +2,12 @@
 // Licensed under the MIT License.
 
 using System;
+using System.Collections.Concurrent;
 using System.Linq;
 using System.Net.Http;
 using System.Security.Cryptography;
 using System.Security.Cryptography.X509Certificates;
+using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.DependencyInjection;
@@ -46,6 +48,81 @@ public void TokenAcquirerFactoryDoesNotUseAspNetCoreHost()
             Assert.Equal("Microsoft.Identity.Web.Hosts.DefaultTokenAcquisitionHost", service.GetType().FullName);
         }
 
+        [Fact]
+        public void DefaultTokenAcquirer_GetKeyHandlesNulls()
+        {
+            var res = DefaultTokenAcquirerFactoryImplementation.GetKey("1", "2", "3");
+            Assert.Equal("123", res);
+
+            var no_region = DefaultTokenAcquirerFactoryImplementation.GetKey("1", "2", null);
+            Assert.Equal("12", no_region);
+        }
+
+        [Fact]
+        public void AcquireToken_WithMultipleRegions()
+        {
+            var tokenAcquirerFactory = TokenAcquirerFactory.GetDefaultInstance();
+            _ = tokenAcquirerFactory.Build();
+
+            ITokenAcquirer tokenAcquirerA = tokenAcquirerFactory.GetTokenAcquirer(
+               authority: "https://login.microsoftonline.com/msidentitysamplestesting.onmicrosoft.com",
+               clientId: "6af093f3-b445-4b7a-beae-046864468ad6",
+               clientCredentials: s_clientCredentials,
+               "US");
+
+            ITokenAcquirer tokenAcquirerB = tokenAcquirerFactory.GetTokenAcquirer(
+               authority: "https://login.microsoftonline.com/msidentitysamplestesting.onmicrosoft.com",
+               clientId: "6af093f3-b445-4b7a-beae-046864468ad6",
+               clientCredentials: s_clientCredentials,
+               "US");
+
+            ITokenAcquirer tokenAcquirerC = tokenAcquirerFactory.GetTokenAcquirer(
+               authority: "https://login.microsoftonline.com/msidentitysamplestesting.onmicrosoft.com",
+               clientId: "6af093f3-b445-4b7a-beae-046864468ad6",
+               clientCredentials: s_clientCredentials,
+               "EU");
+
+            Assert.Equal(tokenAcquirerA, tokenAcquirerB);
+            Assert.NotEqual(tokenAcquirerA, tokenAcquirerC);
+        }
+
+        [Fact]
+        public void AcquireToken_SafeFromMultipleThreads()
+        {
+            var tokenAcquirerFactory = TokenAcquirerFactory.GetDefaultInstance();
+            _ = tokenAcquirerFactory.Build();
+
+            var count = new ConcurrentDictionary<ITokenAcquirer, bool>();
+
+            var action = () =>
+            {
+                for (int i = 0; i < 1000; i++)
+                {
+                    ITokenAcquirer res = tokenAcquirerFactory.GetTokenAcquirer(
+                      authority: "https://login.microsoftonline.com/msidentitysamplestesting.onmicrosoft.com",
+                      clientId: "6af093f3-b445-4b7a-beae-046864468ad6",
+                      clientCredentials: s_clientCredentials,
+                      "" + (i%11));
+
+                    count.TryAdd(res, true);
+                }
+            };
+
+            Thread[] threads = new Thread[16];
+            for (int i = 0; i < 16; i++)
+            {
+                threads[i] = new Thread(() => action());
+                threads[i].Start();
+            }
+
+            foreach (Thread thread in threads)
+            {
+                thread.Join();
+            }
+
+            Assert.Equal(11, count.Count);
+        }
+
         [IgnoreOnAzureDevopsFact]
         //[Theory]
         //[InlineData(false)]