Book excerpt: Flutter is a free and open-source mobile UI framework created by Google. There are other tools for the mobile application developers, but Flutter has distinguished it lately for its one single codebase that runs everywhere. If you learn Flutter, with the help of one programming language Dart, and one single codebase you will be able to create two mobile applications, one for Android and the other for iOS.To start with you need to install Flutter that consists of SDK or Software Development Kit and the framework that consists of User Interface libraries based Widget.This book will teach you from the very beginning - how to install Flutter, what IDE you need and above all, how to build your first mobile application.Because Flutter uses Dart programming language, we will start with Flutter, but side by side we will also learn Dart. We will see how Dart programming concepts are implemented in Flutter.Why you will learn Flutter? It is because, Flutter is much simpler to build mobile applications than other available tools.