The Free Software Foundation has published a short article on relicensing versus license compatibility. The FSF's Licensing and Compliance Lab receives many questions and license violation reports related to projects that had their license changed by a downstream distributor, or that are combined from two or more programs under different licenses. We collaborated with Yoni Rabkin, an experienced and long time FSF licensing volunteer, on an updated version of his article to provide the free software community with a general explanation on how the GNU General Public License (GNU GPL) is intended to work in such situations.