How does the GPL affect my freedom in licensing my plugin or theme?

Most plugin and theme authors choose to license their plugins and themes under the GPL. Also, keep in mind that if your theme or plugin incorporates code from another theme or plugin that uses the GPL, you will probably need to license your theme or plugin with the GPL as well. If your theme or plugin is completely independent of other WordPress code, themes, and plugins, then you can probably license it however you would like.