Xamarin enables developers to write mobile apps using C# and share code across platforms like iOS and Android. Developers can build native user interfaces and take advantage of native performance on each device, while sharing up to 90% of their code. This hybrid approach allows building apps for over 2.5 billion devices using C# and the .NET framework in Visual Studio. Key benefits include writing everything in C#, 100% API coverage on all platforms, and always being up to date with the latest APIs.