This book teaches you how to write clean code. It presents software design and development principles and patterns in a very practical manner. This book is suitable for both junior and senior developers. Basic understanding and knowledge of object-oriented programming in one language, like C++, Java, JavaScript/TypeScript, Python or C# is required. Examples in this book are presented in Java, JavaScript/TypeScript, or C++. Most examples are in Java or JavaScript/ TypeScript and are adaptable to other programming languages, too. The content of this book is divided into eleven chapters.