From what I've seen of the portion of the GPL in question, the definition of "derivative work" is subject to interpretation, in my mind. Something for the lawye

From what I've seen of the portion of the GPL in question, the definition of "derivative work" is subject to interpretation, in my mind. Something for the lawyers to figure out. My 2 cents: Myself, I'm not convinced that a theme is a derivative work. Isn't the API documentation public? Is it not -theoretically- (although impractical) possible to create a theme for Wordpress without having Wordpress itself? (Having said that, it would also be possible to write a non-GPL blogging engine that uses the same API without seeing the Wordpress code) Also, since the theme isn't distributed with Wordpress, I personally think it's harder to argue that it's a derivative piece of work, since none of the original Wordpress code is altered. A better source of information from a legal perspective is the guy at perpetualbeta.com, who delved into this a few months ago with a couple of posts: http://perpetualbeta.com/release/2009/11/why-the-gpl-does-not-apply-to-premium-wordpress-themes/ http://perpetualbeta.com/release/2009/11/why-the-gpl-does-no... http://perpetualbeta.com/release/2009/12/why-the-gplderivative-work-debate-doesnt-matter-for-wordpress-themes/ http://perpetualbeta.com/release/2009/12/why-the-gplderivati... From what I understand, he -is- a lawyer, and he has done intellectual property work, so his opinion, at least on the surface, would seem to have some weight. His position that "fair use" moots the GPL argument is quite interesting.