MIT License

The MIT License is a free software license originating at the Massachusetts Institute of Technology (MIT). It is a permissive free software license, meaning that it puts only very limited restriction on reuse and has therefore an excellent license compatibility. The MIT license permits reuse within proprietary software provided all copies of the licensed software include a copy of the MIT License terms and the copyright notice. The MIT license is also compatible with many copyleft licenses, such as the GPL; MIT licensed software can be integrated into GPL software, but not the other way around.

While the MIT license was always an important and often used license in the FOSS domain, in 2015 according to Black Duck Software and GitHub data, it became the most popular license before GPL variants and other FOSS licenses.

Notable software packages that use one of the versions of the MIT License include Expat, the Mono development platform class libraries, Ruby on Rails, Node.js, jQuery and the X Window System, for which the license was written.