|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, Node.js, Lua (from version 5.0 onwards), Wayland, jQuery and the X Window System, for which the license was written.
- Various versions 1
- License terms 2
- Comparison to other licenses 3
- See also 4
- References 5
- External links 6
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 on the official site of 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.
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:
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 specifically grants the right to "sublicense" in the text of the license itself — a right not mentioned in the BSD license which simply grants the right to "redistribute and use." The right to sublicense means that the party that receives code under the MIT license grant has the legal right to grant all license rights it received downstream to a third party to whom that licensee distributes the MIT code.
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 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."  Any person is ordinarily free to make, use, or sell anything they want, and a grant do so is not needed. What a patent holder has is the right to exclude others from doing what they normally are free to do. So the inclusion of the words granting the right to "use" and "sell" can be construed as meaning no more than the licensee has all the rights they would normally have under a copyright grant. There is no need to infer that these commonly used words mean that the licensor was waiving its patent right to exclude others from such activity (and indeed presumes that the licensor had any such patent rights to exclude to begin with). Whether or not a court might imply a patent grant under the MIT license therefore remains an open question.
The Simplified BSD license used by FreeBSD is essentially identical 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 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.
- Dictionary.com defines "sublicense" as "a license or contract granted to a third party by a licensee for specified rights or uses of a product, brand name, logo, etc." http://dictionary.reference.com/browse/sublicense
- Stern and Allen, Open Source Licensing, p. 495 in Understanding the Intellectual Property License 2013 (Practicing Law Institute 2013)
- 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.
- 35 U.S. Code section 154 at http://www.law.cornell.edu/uscode/text/35/154 Stern and Allen, supra, p. 495
- Bitlaw, 1996-2013 Daniel A. Tysver (Beck & Tysver) http://www.bitlaw.com/patent/rights.html
- MIT License variants
- The MIT License template (Open Source Initiative official site)
- Expat License
- X11 License