Open-sourcing the C# and Visual Basic compilers is one of the most appreciated things by the .NET community, especially as it exposes rich code analysis APIs to analyze and edit code. If you want to use Roslyn API to write powerful extensions and contribute to the C# developer tool chain, then this book is for you. Additionally, if you are just a .NET developer and want to use this rich Roslyn-based functionality in Visual Studio to improve the code quality and maintenance of your code base, then this book is also for you. This book is divided into the following broad modules: 1. Writing and consuming analyzers/fixers (Chapters 1 - 5): You will learn to write different categories of Roslyn analyzers and harness and configure analyzers in your C# projects to catch quality, security and performance issues. Moving ahead, you will learn how to improve code maintenance and readability by using code fixes and refactorings and also learn how to write them. 2. Using Roslyn-based agile development features (Chapters 6 and 7): You will learn how to improve developer productivity in Visual Studio by using features such as live unit testing, C# interactive and scripting. 3. Contributing to the C# language and compiler tool chain (Chapters 8 - 10): You will see the power of open-sourcing the Roslyn compiler via the simple steps this book provides; thus, you will contribute a completely new C# language feature and implement it in the Roslyn compiler codebase. Finally, you will write simple command line tools based on the Roslyn service API to analyze and edit C# code.