This book is for those who will not settle for a black-box approach when working with a database. If you are eager to learn, prefer not to take expert advice for granted, and would like to figure out everything yourself, follow along. I assume that the reader has already tried using PostgreSQL and has at least some general understanding of how it works. Entry-level users may find the text a bit difficult. For example, I will not tell anything about how to install the server, enter psql commands, or set configuration parameters. I hope that the book will also be useful for those who are familiar with another database system, but switch over to PostgreSQL and would like to understand how they differ. A book like this would have saved me a lot of time several years ago. And that’s exactly why I finally wrote it. In the introductory chapter, I briefly touch upon the main database concepts that will serve as the foundation for all the further narration. I do not expect you to get much new information from this chapter but still include it to complete the big picture. Besides, this overview can be found useful by those who are migrating from other database systems.