|Author||Massachusetts Institute of Technology|
|Publisher||Massachusetts Institute of Technology|
|Linking from code with a different license||Yes|
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 permits reuse within proprietary software provided all copies of the licensed software include a copy of the MIT License terms and the copyright notice. Such proprietary software retains its proprietary nature even though it incorporates software under the MIT License. The license is also GPL-compatible, meaning that the GPL permits combination and redistribution with software that uses the MIT License.
Notable software packages that use one of the versions of the MIT License include Expat, the Mono development platform class libraries, Ruby on Rails, Nodejs, Lua (from version 5.0 onwards), Wayland and the X Window System, for which the license was written.
Because MIT has used many licenses for software, "MIT License" is considered ambiguous by the Free Software Foundation. "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 on the official site of Open Source Initiative is the same as the "Expat License".
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.
A common form of the MIT License (from OSI's official site, which is the same version as the "Expat License", and which is not identical to 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.
Comparison to other licenses
The MIT License is similar to the 3-clause "modified" BSD license, except that the BSD license contains a notice prohibiting the use of the name of the copyright holder in promotion. This is sometimes present in versions of the MIT License, as noted above.
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.
The MIT License states more explicitly the rights given to the end-user, including the right to use, copy, modify, merge, publish, distribute, sublicense, and/or sell the software. The MIT license also grants the right to sublicense[clarification needed]—a right not mentioned in the BSD license. Because the MIT license grants the right to sublicense, any distributor of MIT-licensed code has the right to grant a license to the entire code base,[dubious ] including components that were originally licensed under the MIT license by third parties. The MIT license also includes a warranty of non-infringement entirely lacking in the BSD license.[clarification needed] This is important to relieve contributors of the nearly insurmountable burden of being certain that the software they are making available under the MIT license is not infringing some parties' patent or copyright. 
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.  The MIT license contains terms that blur[clarification needed] the legal line between copyright and patent grants such as "deal in," "use," and "sell."  Whether a court might imply a patent grant under the MIT license remains an open question.
The Simplified BSD license used by FreeBSD is essentially identical[discuss] to the MIT License, as it contains neither an advertising clause, nor a prohibition on promotional use of the copyright holder's name.
Also similar in terms is the ISC license, which has a simpler language.
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.
- Lawrence Rosen, OPEN SOURCE LICENSING, p.85 (Prentice Hall PTR, 1st ed. 2004)
- Various Licenses and Comments about Them – GNU Project – Free Software Foundation. Gnu.org (1999-09-03). Retrieved on 2013-07-17.
- Stallman, Richard. "Various Licenses and Comments about Them # Expat License". Free Software Foundation. Retrieved 5 December 2010.
- Stallman, Richard. "Various Licenses and Comments about Them # X11 License". Free Software Foundation. Retrieved 5 December 2010.
- "Open Source Initiative OSI – The MIT License:Licensing". Open Source Initiative. Retrieved 5 December 2010.
- Dickey, Thomas E. "NCURSES — Frequently Asked Questions (FAQ)".
- "To All Licensees, Distributors of Any Version of BSD". University of California, Berkeley. 1999-07-22. Retrieved 2006-11-15.
- See, Lawrence Rosen, Open Source Licensing p. 90 (Prentice Hall PTR, 1st ed. 2004)
- Stern and Allen, Open Source Licensing, p. 495 in Understanding the Intellectual Property License 2013 (Practicing Law Institute 2013)
- Stern and Allen, supra, p. 495
- Christian H. Nadan, Closing the Loophole; Open Source Licensing and the Implied Patent License, THE COMPUTER AND INTERNET LAWYER, Vol. 26, No. 8 (Aug. 2009) available at http://www.scribd.com/doc/46088081/Closing-the-Loophole-Open-Source-Licensing-and-the-Implied-Patent-License-Nadan who argues that “By using patent terms like “deal in,” “use,” and “sell,” the MIT license grant is more likely to be deemed to include express patent rights than the BSD license.
- MIT License variants
- The MIT License template (Open Source Initiative official site)
- Expat License
- X11 License