Xamarin.Android is used to build applications for Android with .NET, and contains the bindings to the Android APIs. The Mono runtime and the Android runtime run side by side on top of a Linux kernel. Xamarin.Android applications could either be just-in-time (JIT)-compiled or AOT-compiled, but to AOT-compile them, you need to use Visual Studio Enterprise.
Communication between the Mono runtime and the Android runtime occurs via a Java Native Interface (JNI) bridge. There are two types of JNI bridges: manage callable wrapper (MCW) and Android callable wrapper (ACW). An MCW is used when the code needs to run in the Android runtime (ART) and an ACW is used when ART needs to run code in the Mono runtime, as shown in the following diagram: