Visual Studio Users: If you're running Mono for Android 1.9.1 or later, you should be prompted to update. Otherwise, download monoandroid-4.0.1.msi and install.

MonoDevelop Users: You should be prompted to upgrade next time you open MonoDevelop, or you can use Help > Check for Updates. IDE support requires MonoDevelop 2.8.4.1.

GC Stability Improvements: We've fixed an assert within the GC and improved stability when invoking GC.Collect().

UsesLibraryAttribute and UsesPermissionAttribute constructor parameters: In 4.0.0, UsesLibraryAttributeand UsesPermissionAttribute required that you use the Name property. Now you may use the constructor:

[assembly: UsesLibrary (Android.Manifest.Permission.Internet)]

Library project defines: Library projects now get the same set of ANDROID defines as Application projects.

• Additional int to enumeration parameter and return type conversions.

• API Level 4: Mono.Android.dll , Mono.Android.GoogleMaps.dll , OpenTK.dll
• API Level 7: Mono.Android.dll , Mono.Android.GoogleMaps.dll , OpenTK.dll
• API Level 8: Mono.Android.dll , Mono.Android.GoogleMaps.dll , OpenTK.dll
• API Level 10: Mono.Android.dll , Mono.Android.GoogleMaps.dll , OpenTK.dll
• API Level 12: Mono.Android.dll , Mono.Android.GoogleMaps.dll , OpenTK.dll
• API Level 14: Mono.Android.dll , Mono.Android.GoogleMaps.dll , OpenTK.dll

• 2091 : Assertion at ../../../../mono/metadata/sgen-bridge.c:426, condition `!entry->is_bridge' not met
• 2137 : Provide ANDROID defines for class libraries
• 2206 : DataContractJsonSerializer does not work
• 2326 : Calling GC.Collect() repeatedly hangs app
• 2349 : Assertion at ../../../../mono/metadata/sgen-bridge.c:426, condition `!entry->is_bridge' not met
• 2367 : Invalid Java generated for constructors that call base with different parameters
• Fixed java.lang.NoClassDefFoundError when creating arrays of various types.
• The <AndroidResgenFile/> element no longer requires a directory to be specified.
• Several Android Callable Wrapper constructor generation fixes.

Warning: Samsung shipped a broken kernel with Android 2.1, which is not able to support JIT compilation. If you possess a Galaxy-class device with Android 2.1, you will get unexpected results, this is caused by a kernel bug that breaks cache coherency, rendering any engine doing JIT compilation useless. Check with your manufacturer/carrier for an Android 2.2 update.