This document discusses Windows Phone 7 and its development tools. It outlines the key principles of the Windows Phone 7 user interface including being clean, content-focused, integrating hardware and software seamlessly, using world-class motion, and having a soulful and alive feel. It also discusses the screen resolution and orientation, fonts, navigation and pages, scrolling, themes, input methods, and hardware buttons. For development, it covers using Silverlight for applications and games, XNA for games, and Windows Live for push notifications and location services. It also outlines the Windows Phone Marketplace for publishing applications and resources for Windows Phone design and development.