This document discusses building mobile apps with Xamarin and Visual Studio App Center. It describes how Xamarin enables code sharing across platforms using familiar languages and libraries while still allowing access to native device functionality. It compares classic Xamarin vs Xamarin Forms approaches and outlines the features of Visual Studio App Center, which provides a unified experience for building, testing, distributing and monitoring mobile apps in one place. It includes a demo of setting up a new application in App Center.