The book "Crystal Programming: An Introduction to Creating Efficient, Secure, and Intelligible Web and CLI Applications" is a collection of information that will help the reader enter the exciting world of Crystal programming. The authors of the book cover in detail the design and development of both web and command-line applications, providing the reader with the necessary knowledge to create efficient and secure applications. In this book, you will find comprehensive explanations of the basic concepts of the Crystal language, tools for working with this programming language, as well as examples of practical tasks that will help you learn the best practices of software development. Each chapter is distilled down to detail so that the reader can master every aspect of Crystal programming step by step. "Programming in Crystal. An introduction to creating efficient, secure and understandable web and CLI applications" is an excellent guide for those who want to deepen their knowledge of this young but promising programming language and create quality applications for various application areas.