The document provides an introduction to Windows 8 mobile app development. It discusses key facts about Windows 8 and Windows Phone, such as there being over 100 million Windows 8 licenses sold to date and the Windows Phone Store featuring over 170,000 apps. The document outlines advantages of developing a single app for all Windows devices and highlights shared components between Windows 8 and Windows Phone like the core OS. It also reviews the development environment, APIs, and differences between the two platforms like available controls and screen sizes. Missing features in early versions like a task manager and file manager are also noted.