Lightning is a routable network of payment channels that provides secure, cheap, fast Bitcoin payments with a high degree of solvency, even when it comes to small amounts. This book provides an overview of the Lightning network, the basic concepts that formed its basis, and the principles of work. The examples are illustrated in Go, C++, Python and using the Unix-like operating system command line. The book is addressed to programmers who have an idea of ​ ​ the basics of the Bitcoin system, but a number of chapters are available to a wide range of readers interested in block chains.