##License Plugins under a GPL Compatible License
Plug-ins and themes *should* be licensed under a WordPress-compatible license. This enables them to be re-distributed with WordPress as a "program." A recommended license is [the GPL][1]. *Take care that all code libraries included with the plug-in are compatible with the same license.*

(This has [been a problem][2] and serious [point of debate][3] both in the past and [present][4].) 


  [1]: http://www.gnu.org/licenses/gpl.html
  [2]: http://wordpress.stackexchange.com/questions/377/gpl-and-plugins
  [3]: http://wordpress.stackexchange.com/questions/5/am-i-allowed-to-license-my-wordpress-theme-under-the-agpl
  [4]: http://core.trac.wordpress.org/ticket/14685