DFSG compatible Yes OSI approved Yes Copyleft No | FSF approved Yes GPL compatible Yes | |
Publisher Massachusetts Institute of Technology | ||
The MIT License is a permissive free software license originating at the Massachusetts Institute of Technology (MIT). As a permissive license, it puts only very limited restriction on reuse and has, therefore, an excellent license compatibility. The MIT license permits reuse within proprietary software provided that 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 GNU General Public License (GPL); MIT licensed software can be integrated into GPL software, but not the other way around.
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As of 2015, it is the most popular software license, ahead of any GPL variant and other Free and open-source software (FOSS) licenses. Notable projects that use one of the versions of the MIT License include Ruby on Rails, Node.js, jQuery, and the X Window System.
License terms
A common form of the MIT License (from the OSI's website, which is the same version as the "Expat License", and which is not identical to the license used in the X source code) is defined as follows:
Copyright (c) <year> <copyright holders> Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), 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:
Copyright (C) <date> X Consortium Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), 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.Variants
Because MIT has used many licenses for software, the Free Software Foundation considers "MIT License" ambiguous. "MIT License" may refer to the "Expat License" (used for Expat) or to the "X11 License" (also called "MIT/X Consortium License"; used for the X Window System by the MIT X Consortium). The "MIT License" published by the Open Source Initiative is the same as the "Expat License".
Differing from the Expat License, the X11 License and the "MIT License" chosen for ncurses by the Free Software Foundation include the clause:
Except as contained in this notice, the name(s) of the above copyright holders shall not be used in advertising or otherwise to promote the sale, use or other dealings in this Software without prior written authorization.
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" (since disavowed by UC Berkeley) is present in the modified MIT License used by XFree86.
Like the BSD license the MIT license does not include an express patent license. Both the BSD and the MIT licenses were drafted before the patentability of software was generally recognized under US law. A similarly permissive license, which includes an explicit contributor's patent license, is the Apache license version 2.0+.
The MIT license contains terms that are used in defining the rights of a patent holder in 35 U.S Code section 154 namely "use", and "sell". This has been construed by some commentators. 35 U.S. Code section 154 defines the right of a patent holder as follow: "Every patent shall contain a short title of the invention and a grant to the patentee, his heirs or assigns, of the right to exclude others from making, using, offering for sale, or selling the invention throughout the United States or importing the invention into the United States..." The nature of the right conferred by a U.S. patent is not obvious at first, because it is a negative right, the key is in the words "right to exclude".
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.
Reception
As of 2015, according to Black Duck Software and GitHub, the MIT license was the most popular free software license, with the GNU GPLv2 coming second. In June 2016 an analysis of the Fedora Project's packages revealed the MIT as most used license.
Notable projects that use one of the versions of the MIT License include Expat, an XML parser library; Ruby on Rails, a web application framework; Node.js, a web application runtime environment; jQuery, a JavaScript library; the Lua programming language; and the X Window System, for which the license was originally written.