diff --git a/src/TestableIO.System.IO.Abstractions.TestingHelpers/MockFile.cs b/src/TestableIO.System.IO.Abstractions.TestingHelpers/MockFile.cs
index 5ec85d35f..ad8a0f005 100644
--- a/src/TestableIO.System.IO.Abstractions.TestingHelpers/MockFile.cs
+++ b/src/TestableIO.System.IO.Abstractions.TestingHelpers/MockFile.cs
@@ -424,7 +424,15 @@ public override DateTime GetLastWriteTimeUtc(SafeFileHandle fileHandle)
         /// <inheritdoc />
         public override UnixFileMode GetUnixFileMode(string path)
         {
-            throw CommonExceptions.NotImplemented();
+            mockFileDataAccessor.PathVerifier.IsLegalAbsoluteOrRelative(path, "path");
+
+            if (!mockFileDataAccessor.FileExists(path))
+            {
+                throw CommonExceptions.FileNotFound(path);
+            }
+            
+            var mockFileData = mockFileDataAccessor.GetFile(path);
+            return mockFileData.UnixMode;
         }
 #endif
 
@@ -954,7 +962,15 @@ public override void SetLastWriteTimeUtc(SafeFileHandle fileHandle, DateTime las
         /// <inheritdoc />
         public override void SetUnixFileMode(string path, UnixFileMode mode)
         {
-            throw CommonExceptions.NotImplemented();
+            mockFileDataAccessor.PathVerifier.IsLegalAbsoluteOrRelative(path, "path");
+
+            if (!mockFileDataAccessor.FileExists(path))
+            {
+                throw CommonExceptions.FileNotFound(path);
+            }
+            
+            var mockFileData = mockFileDataAccessor.GetFile(path);
+            mockFileData.UnixMode = mode;
         }
 #endif
 
diff --git a/src/TestableIO.System.IO.Abstractions.TestingHelpers/MockFileData.cs b/src/TestableIO.System.IO.Abstractions.TestingHelpers/MockFileData.cs
index e77e214da..7fcf94514 100644
--- a/src/TestableIO.System.IO.Abstractions.TestingHelpers/MockFileData.cs
+++ b/src/TestableIO.System.IO.Abstractions.TestingHelpers/MockFileData.cs
@@ -201,6 +201,16 @@ public FileSecurity AccessControl
         /// Gets or sets the File sharing mode for this file, this allows you to lock a file for reading or writing.
         /// </summary>
         public FileShare AllowedFileShare { get; set; } = FileShare.ReadWrite | FileShare.Delete;
+
+#if FEATURE_UNIX_FILE_MODE
+        /// <summary>
+        /// Gets or sets the Unix file mode (permissions) for this file.
+        /// This allows you to configure the read, write and execute access for user, group and other.
+        /// </summary>
+        public UnixFileMode UnixMode { get; set; } = UnixFileMode.UserRead | UnixFileMode.GroupRead |
+                                                     UnixFileMode.OtherRead | UnixFileMode.UserWrite;
+#endif
+
         /// <summary>
         /// Checks whether the file is accessible for this type of FileAccess. 
         /// MockFileData can be configured to have FileShare.None, which indicates it is locked by a 'different process'.
diff --git a/tests/TestableIO.System.IO.Abstractions.TestingHelpers.Tests/MockFileGetUnixFileModeTests.cs b/tests/TestableIO.System.IO.Abstractions.TestingHelpers.Tests/MockFileGetUnixFileModeTests.cs
new file mode 100644
index 000000000..85fd7b35c
--- /dev/null
+++ b/tests/TestableIO.System.IO.Abstractions.TestingHelpers.Tests/MockFileGetUnixFileModeTests.cs
@@ -0,0 +1,59 @@
+#if FEATURE_UNIX_FILE_MODE
+using System.Runtime.Versioning;
+
+namespace System.IO.Abstractions.TestingHelpers.Tests
+{
+    using Collections.Generic;
+
+    using NUnit.Framework;
+
+    using XFS = MockUnixSupport;
+
+    [UnsupportedOSPlatform("windows")]
+    [UnixOnly("This feature is not supported on Windows.")]
+    public class MockFileGetUnixFileModeTests
+    {
+        [Test]
+        public void MockFile_GetUnixFileMode_ShouldReturnDefaultAccessMode()
+        {
+            // Arrange
+            var expected = UnixFileMode.UserRead | 
+                           UnixFileMode.GroupRead | 
+                           UnixFileMode.OtherRead | 
+                           UnixFileMode.UserWrite;
+            
+            var fileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
+            {
+                { XFS.Path(@"C:\something\some.txt"), new MockFileData("Demo text content") }
+            });
+
+            // Act
+            var result = fileSystem.File.GetUnixFileMode(XFS.Path(@"C:\something\some.txt"));
+
+            // Assert
+            Assert.That(result, Is.EqualTo(expected));
+        }
+        
+        [Test]
+        public void MockFile_GetUnixFileMode_ShouldReturnSpecifiedAccessMode([Values] UnixFileMode unixFileMode)
+        {
+            // Arrange
+            var mockFileData = new MockFileData("Demo text content")
+            {
+                UnixMode = unixFileMode
+            };
+            
+            var fileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
+            {
+                { XFS.Path(@"C:\something\some.txt"), mockFileData }
+            });
+
+            // Act
+            var result = fileSystem.File.GetUnixFileMode(XFS.Path(@"C:\something\some.txt"));
+
+            // Assert
+            Assert.That(result, Is.EqualTo(unixFileMode));
+        }
+    }
+}
+#endif
\ No newline at end of file
diff --git a/tests/TestableIO.System.IO.Abstractions.TestingHelpers.Tests/MockFileSetUnixFileModeTests.cs b/tests/TestableIO.System.IO.Abstractions.TestingHelpers.Tests/MockFileSetUnixFileModeTests.cs
new file mode 100644
index 000000000..02f944c8a
--- /dev/null
+++ b/tests/TestableIO.System.IO.Abstractions.TestingHelpers.Tests/MockFileSetUnixFileModeTests.cs
@@ -0,0 +1,53 @@
+#if FEATURE_UNIX_FILE_MODE
+using System.Runtime.Versioning;
+
+namespace System.IO.Abstractions.TestingHelpers.Tests
+{
+    using Collections.Generic;
+
+    using NUnit.Framework;
+
+    using XFS = MockUnixSupport;
+
+    [UnsupportedOSPlatform("windows")]
+    [UnixOnly("This feature is not supported on Windows.")]
+    public class MockFileSetUnixFileModeTests
+    {
+        [Test]
+        public void MockFile_SetUnixFileMode_ShouldSetSpecifiedAccessMode([Values] UnixFileMode unixFileMode)
+        {
+            // Arrange
+            var mockFileData = new MockFileData("Demo text content");
+            var fileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
+            {
+                { XFS.Path(@"C:\something\some.txt"), mockFileData }
+            });
+
+            // Act
+            fileSystem.File.SetUnixFileMode(XFS.Path(@"C:\something\some.txt"), unixFileMode);
+
+            // Assert
+            Assert.That(mockFileData.UnixMode, Is.EqualTo(unixFileMode));
+        }
+        
+        [TestCase(UnixFileMode.UserRead | UnixFileMode.GroupRead | UnixFileMode.OtherRead)]
+        [TestCase(UnixFileMode.UserRead | UnixFileMode.UserWrite | UnixFileMode.UserExecute)]
+        [TestCase(UnixFileMode.UserExecute | UnixFileMode.OtherWrite | UnixFileMode.GroupRead)]
+        public void MockFile_SetUnixFileMode_ShouldSetSpecifiedAccessModeFlags(UnixFileMode unixFileMode)
+        {
+            // Arrange
+            var mockFileData = new MockFileData("Demo text content");
+            var fileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
+            {
+                { XFS.Path(@"C:\something\some.txt"), mockFileData }
+            });
+
+            // Act
+            fileSystem.File.SetUnixFileMode(XFS.Path(@"C:\something\some.txt"), unixFileMode);
+
+            // Assert
+            Assert.That(mockFileData.UnixMode, Is.EqualTo(unixFileMode));
+        }
+    }
+}
+#endif
\ No newline at end of file
diff --git a/version.json b/version.json
index faa1bcb8f..081fbf157 100644
--- a/version.json
+++ b/version.json
@@ -1,6 +1,6 @@
 {
   "$schema": "https://raw.githubusercontent.com/AArnott/Nerdbank.GitVersioning/master/src/NerdBank.GitVersioning/version.schema.json",
-  "version": "21.0",
+  "version": "21.1",
   "assemblyVersion": {
     "precision": "major"
   },