Permissive Free Software Licence

A permissive free software licence is a class of free software licence with minimal requirements about how the software can be redistributed. This is in contrast to copyleft licences, which have reciprocity / share-alike requirements. Both sets of free software licences offer the same freedoms in terms of how the software can be used, studied, and privately modified. A major difference is that when the software is being redistributed (either modified or unmodified), permissive licences permit the redistributor to combine the licensed material with other licence terms, potentially adding further restrictions to a derived work, while copyleft licences do not allow further restrictions (among other possible differences). The term "permissive" as applied to software licensing is sometimes debatable in terms of specific terms and requirements, with occasional references to very weak copyleft being described as "permissive". A more narrowly constrained term related to permissive licensing is copyfree, which implies distinct licence term requirements analogous to, but different from, those of free software.

Well-known examples of permissive free software licences include the MIT License and the BSD licences. A well known copyleft licence is the GNU General Public License.