MIT License
The MIT License is a permissive free software license originating at the Massachusetts Institute of Technology in the late 1980s. As a permissive license, it puts only very limited restriction on reuse and has, therefore, high license compatibility.
It is compatible because it can be re-licensed under other licenses. The MIT license is compatible with many copyleft licenses, such as the GNU General Public License ; MIT licensed software can be re-licensed as GPL software, and integrated with other GPL software, but not the other way around. The MIT license also permits reuse within proprietary software, provided that either all copies of the licensed software include a copy of the MIT License terms and the copyright notice, or the software is re-licensed to remove this requirement. MIT-licensed software can also be re-licensed as proprietary software, which distinguishes it from copyleft software licenses., MIT was the most popular software license found in one analysis, continuing from reports in 2015 that MIT was the most popular software license on GitHub, ahead of any GPL variant and other free and open-source software licenses.
Notable projects that use the MIT License include the X Window System, Ruby on Rails, Node.js, Lua and jQuery. Notable companies using the MIT license include Microsoft and Facebook.
License terms
A common form of the MIT License is this :Copyright
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files, to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
An intermediate form of license used by the X Consortium for X11 used the following wording:
CopyrightX Consortium
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files, to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE X CONSORTIUM BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
Except as contained in this notice, the name of the X Consortium shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization from the X Consortium.
X Window System is a trademark of X Consortium, Inc.
Ambiguity and variants
Because the MIT has been using many licenses for software since its creation, saying "the MIT License" is ambiguous. For example, the MIT offers several licensing options for FFTW."MIT License" may refer to the Expat License or to the X11 License. The "MIT License" published by the Open Source Initiative is the same as the "Expat License".
The X11 License and the "MIT License" chosen for ncurses by the Free Software Foundation both include the following clause, absent in the Expat License:
Comparison to other licenses
The original BSD license also includes a clause requiring all advertising of the software to display a notice crediting its authors. This "advertising clause" is present in the modified MIT License used by XFree86.The University of Illinois/NCSA Open Source License combines text from both the MIT and BSD licenses; the license grant and disclaimer are taken from the MIT License.
The ISC license contains similarities to both the MIT and simplified BSD licenses, the biggest difference being that language deemed unnecessary by the Berne Convention is omitted.
Relation to patents
Like the BSD license, the MIT license does not include an express patent license although some commentators state that the grant of rights covers all potential restrictions including patents. Both the BSD and the MIT licenses were drafted before the patentability of software was generally recognized under US law. The Apache License version 2.0 is a similarly permissive license that includes an explicit contributor's patent license.In the US, the MIT license contains the terms "use" and "sell" that are used in defining the rights of a patent holder in 35 U.S. Code section 154. This has been construed by some commentators as an implicit but badly-written license in the US to use any underlying patents.