This document introduces Flutter, an open-source mobile application development framework created by Google. It discusses why hybrid mobile apps are useful, and how Flutter addresses this through its ability to write once and deploy to both Android and iOS. Key features of Flutter that are highlighted include it being owned by Google, using the Dart programming language, and its widget-based architecture. The document then provides an overview of various Flutter development topics such as code editors, state management, animations, plugins, and profiling.