If WordPress were a country, our Bill of Rights would be the GPL because it protects our core freedoms. We’ve always done our best to keep WordPress.org clean and only promote things that are completely compatible and legal with WordPress’s license. There have been some questions in the community about whether the GPL applies to themes like we’ve always assumed. To help clarify this point, I reached out to the Software Freedom Law Center, the world’s preeminent experts on the GPL, which spent time with WordPress’s code, community, and provided us with an official legal opinion. One sentence summary: PHP in WordPress themes must be GPL, artwork and CSS may be but are not required.
