I am not a lawyer either, but: > When you add a license, is the codebase “licensed going forward” or does the code at the revision behind the “added license” c

I am not a lawyer either, but: > When you add a license, is the codebase “licensed going forward” or does the code at the revision behind the “added license” commit not have the license applied? I believe verdverm is right. Unless you make an explicit announcement somehow about previous versions, your licence document would be taken to apply only to the version(s) of the software that bundle that licence document. > curious what happens if the license is changed Same principle applies. You could explicitly re-license the old versions of your software under the new licence as well. > follow up question: licensing per-file vs licensing per codebase I think you'd be on fairly safe legal ground just including a licence document with your project, but GNU recommend you include a short notice in every file in your project, directing the reader to the full text of the licence. [0] [0] https://www.gnu.org/licenses/gpl-howto.en.html https://www.gnu.org/licenses/gpl-howto.en.html