This book is a collaborative effort between several PHP developers to better document and describe how PHP works internally.

There are three primary goals of this book:

  • Document and describe how PHP internals work.

  • Document and describe how to extend the language with extensions.

  • Document and describe how you can interact with the community to develop PHP itself.

This book is primarily targeted at developers who have experience in the C programming language. However, where-ever possible we will attempt to distill the information and summarize it so that developers who don’t know C well, will still be able to understand the content.


Some of the introductory chapters have not been written yet (in particular the ones on creating basic extensions and declaring functions), so if you’re completely new to PHP extension development you’ll have to wait until the remaining introductory chapters are published or start off with other resources on the topic.

The repository for this book is available on GitHub. Please report issues and provide feedback on the issue tracker.