The ultimate guide to Crystal programming covering all its fundamental concepts such as OOP and concurrent programming to help you write readable and safe code and build fast applications Crystal is a programming language with a concise and user-friendly syntax, along with a seamless system and a performant core, reaching C-like speed. This book will help you gain a deep understanding of the fundamental concepts of Crystal and show you how to apply them to create various types of applications. This book comes packed with step-by-step explanations of essential concepts and practical examples. You'll learn how to use Crystal's features to create complex and organized projects relying on OOP and its most common design patterns. As you progress, you'll gain a solid understanding of both the basic and advanced features of Crystal. This will enable you to build any application, including command-line interface (CLI) programs and web applications using IOs, concurrency and C bindings, HTTP servers, and the JSON API. By the end of this programming book, you'll be equipped with the skills you need to use Crystal programming for building and understanding any application you come across. Developers who want to learn Crystal programming or anyone looking to improve their ability to solve real-world problems using the language will find this book helpful. Experience in application development using any other programming language is expected. However, prior knowledge of Crystal is not required.