If you’re itching to go deeper into the legal aspects of navigating WordPress’ relationship to the GPL license, Richard Best has recently made his ebook (and the audio version) called “A Practical Guide to WordPress and the GPL” available for free. Best, a technology and public lawyer based in New Zealand, had previously sold the book with other products as part of a business package that is still available for purchase. After receiving feedback on his most recent post titled “Taking GPL’d code proprietary,” he found that the issues addressed in the book are still relevant and decided to release it for free.

The first two sections provide a brief history of WordPress, its adoption of the GPL, and a summary of the license. These sections are a bit dry, but Chapter 3 is where it gets more interesting, particularly for theme and plugin developers who have questions about licensing GPL-derivatives. Best explores the practical application of the GPL in common business scenarios:

  • If I modify the core WordPress software or a GPL’d theme or plugin, must I release the source code of the modified versions(s) to the public?
  • I’m a theme/plugin developer. I’ve put huge effort into writing my theme/plugin and I’m going to release it under the GPL but I want to make sure that everyone who receives my theme or plugin, even if from someone else, is obliged to pay me a licensing fee or notify me that they have it. Can I do that?
  • I’ve purchased some fully GPL’d themes or plugins from a commercial theme or plugin provider. May I sell those themes or plugins from my own website for my own benefit or publish those themes or plugins on my own website and give them away for free?

Subsequent chapters cover controversies surrounding “GPL non-compliant” sales models, applications of copyright law, GPL compatibility with other licenses, and trademarks. Both the audio and the PDF ebook are available for download on Best’s website. The text of the book is licensed under the Creative Commons Attribution 4.0 International License.