DEAR READER, thank you for picking up this book. WordPress is the most popular self‐hosted website software in use today. It is available as an open source project, licensed under the GPL, and is built largely on top of the MySQL database and PHP programming language. Any server environment that supports that simple combination can run WordPress, making it remarkably portable as well as simple to install and operate. You don’t need to be a systems administrator, developer, HTML expert, or design aesthete to use WordPress. On the other hand, because WordPress has been developed using a powerful set of Internet standard platforms, it can be extended and tailored for a wide variety of applications. WordPress is the publishing mechanism underneath millions of individual blog voices and the engine that powers high‐volume, high‐profile sites such as CNN’s websites and blogs. It was designed for anyone comfortable navigating a browser, but is accessible to web designers and developers as well. Given that range of applications and capabilities, it can prove hard to know where to start if you want to make use of the power of WordPress for your specific purposes. Should you first study the database models and relationships of content and metadata, or the presentation mechanics that generate the HTML output? This book was designed for readers to develop a knowledge of WordPress from the inside out, focusing on the internal structure and flow of the core code as well as the data model on which that code operates. Knowing how something works often makes you more adept at working with it, extending it, or fixing it when it breaks. Just as a race car driver benefits from a fundamental knowledge of combustion engines, aerodynamics, and the mechanics of automobile suspension, someone driving WordPress through its full dynamic range will be significantly more adept once acquainted with the underlying software physics.