MIT License

The MIT License is a permissive free software license originating at the Massachusetts Institute of Technology (MIT)[6] in the late 1980s.[7] As a permissive license, it puts only very limited restriction on reuse and has, therefore, high license compatibility.[8][9]

MIT License
PublisherMassachusetts Institute of Technology
SPDX identifierMIT
(see list for more)[1]
Debian FSG compatibleYes[2]
FSF approvedYes[3][4]
OSI approvedYes[5]
GPL compatibleYes[3][4]
CopyleftNo[3][4]
Linking from code with a different licenceYes

The MIT License is compatible with many copyleft licenses, such as the GNU General Public License (GNU GPL). Any software licensed under the terms of the MIT License can be integrated with software licensed under the terms of the GNU GPL.[10] Unlike copyleft software licenses, the MIT License also permits reuse within proprietary software, provided that all copies of the software or its substantial portions include a copy of the terms of the MIT License and also a copyright notice.[9][11] As of 2020, the MIT License was the most popular software license found in one analysis,[12] continuing from reports in 2015 that the MIT License was the most popular software license on GitHub.[13]

Notable projects that use the MIT License include the X Window System, Ruby on Rails, Nim, Node.js, Lua, and jQuery. Notable companies using the MIT License include Microsoft (.NET Core), Google (Angular), and Meta (React).

License terms

The MIT License has the identifier MIT in the SPDX License List.[14][15] It is also known as the "Expat License".[3] It has the following terms:[16]

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.

Variations

X11 License

The X11 License, a variation of the MIT License, has the identifier X11 in the SPDX License List.[17][4] It is also known as the "MIT/X Consortium License" by the X Consortium (for X11).[18] It has the following terms:[19]

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.

FPA License

The FPA License, a less-permissive variation of the MIT License, has the identifier FPA in the SPDX License List. The main purpose of this license is to limit commercialization of the original software while still allowing educational and personal rights. It has the following terms:[20]

Copyright <YEAR> <COPYRIGHT HOLDER>

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 limitation in the rights to use, copy, modify, merge, publish, and/ or distribute copies of the Software in an educational or personal context, 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.

Permission is granted to sell and/ or distribute copies of the Software in a commercial context, subject to the following conditions:

- Substantial changes: adding, removing, or modifying large parts, shall be developed in the Software. Reorganizing logic in the software does not warrant a substantial change. 

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.

MIT No Attribution License
MIT No Attribution License
AuthorRoman Mamedov, Amazon Web Services
Published28 March 2018
SPDX identifierMIT-0
Debian FSG compatiblen/a
FSF approvedn/a
OSI approvedYes[21]
GPL compatibleYes
CopyleftNo
Linking from code with a different licenceYes
Websitehttps://github.com/aws/mit-0

The MIT No Attribution License, a variation of the MIT License, has the identifier MIT-0 in the SPDX License List.[22] A request for legacy approval to the Open Source Initiative was filed on May 15, 2020,[23] which led to a formal approval on August 5, 2020.[21] By doing so, it forms a public-domain-equivalent license, the same way as BSD Zero Clause. It has the following terms:

MIT No Attribution

Copyright <YEAR> <COPYRIGHT HOLDER>

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.

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.

Other variations

The SPDX License List contains extra MIT license variations. Examples include:[1]

  • MIT-advertising, a variation with an additional advertising clause.

Ambiguity and variants

The name "MIT License" is potentially ambiguous. The Massachusetts Institute of Technology has been using many licenses for software since its creation; for example, MIT offers four licensing options for the FFTW[24] C source code library, one of which is the GPL v2.0 and the other three of which are not open-source. The term "MIT License" has also been used to refer to the Expat License (used for the XML parsing library Expat) and to the X11 License (also called "MIT/X Consortium License"; used for X Window System by the MIT X Consortium).[3] Furthermore, the "MIT License" as published by the Open Source Initiative is the same as the Expat License.[15] Due to this differing use of terms, some prefer to avoid the name "MIT License".[7] The Free Software Foundation argues that the term is misleading and ambiguous, and recommends against its use.[3]

The X Consortium was dissolved late in 1996, and its assets transferred to The Open Group,[25] which released X11R6 initially under the same license. The X11 License[4] and the X11R6 "MIT License" chosen for ncurses by the Free Software Foundation[26] both include the following clause, absent in the Expat License:[3]

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.

As of 2020, the successor to the X Window System is the X.Org Server, which is licensed under what is effectively the common MIT license, according to the X.org licensing page:[27]

The X.Org Foundation has chosen the following format of the MIT License as the preferred format for code included in the X Window System distribution. This is a slight variant of the common MIT license form published by the Open Source Initiative

The "slight variant" is the addition of the phrase "(including the next paragraph)".

The license-management features at popular source code repository GitHub, as well as its "Choose a License" service, do not differentiate between MIT/Expat license variants. The text of the Expat variant is presented as simply the "MIT License" (represented by the metadata tag mit).[28][29]

Comparison to other licenses

BSD

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[30]) 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.[31][32]

GNU GPL

The GNU GPL is explicit about the patent grant an author would be giving when the code (or derivative work) is distributed,[33] the MIT license does not discuss patents. Moreover, the GPL license impacts derivative works, but the MIT license does not.

Relation to patents

Like the BSD license, the MIT license does not include an express patent license although some commentators[34][35] 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.[36] The Apache License version 2.0[3] is a similarly permissive license that includes an explicit contributor's patent license. Of specific relevance to US jurisdictions, the MIT license uses the terms "sell" and "use" that are also used in defining the rights of a patent holder in Title 35 of the United States Code section 154. This has been construed by some commentators[37][38] as an unconventional but implicit license in the US to use any underlying patents.

Origins

One of the originators of the MIT license, computer scientist Jerry Saltzer, has published his recollections of its early development, along with documentary evidence.[39][7]

Reception

As of 2020, according to WhiteSource Software[12] the MIT license was used in 27% of four million open source packages. As of 2015, according to Black Duck Software[40] and a 2015 blog[13] from GitHub, the MIT license was the most popular free software license, with the GNU GPLv2 coming second in their sample of repositories.

See also
  • Comparison of free and open-source software licenses
  • ISC license – similar to the MIT license, but with language deemed unnecessary removed
  • Category:Software using the MIT license

References
  1. "SPDX License List". spdx.org. SPDX Working Group.
  2. "License information". The Debian Project. Software in the Public Interest (published July 12, 2017). 1997–2017. Archived from the original on July 20, 2017. Retrieved July 20, 2017. This page presents the opinion of some debian-legal contributors on how certain licenses follow the Debian Free Software Guidelines (DFSG). ... Licenses currently found in Debian main include: ... Expat/MIT-style licenses ...
  3. "Various Licenses and Comments about Them". The GNU Project. Free Software Foundation (published April 4, 2017). 2014–2017. Expat License. Archived from the original on July 20, 2017. Retrieved July 20, 2017. This is a lax, permissive non-copyleft free software license, compatible with the GNU GPL. It is sometimes ambiguously referred to as the MIT License.
  4. "Various Licenses and Comments about Them". The GNU Project. Free Software Foundation (published April 4, 2017). 2014–2017. X11 License. Archived from the original on July 20, 2017. Retrieved July 20, 2017. This is a lax permissive non-copyleft free software license, compatible with the GNU GPL. ... This license is sometimes called the MIT license, but that term is misleading, since MIT has used many licenses for software.
  5. "Licenses by Name". Open Source Initiative. n.d. Archived from the original on July 20, 2017. Retrieved July 20, 2017. The following licenses have been approved by the OSI. ... MIT License (MIT) ...
  6. Lawrence Rosen, OPEN SOURCE LICENSING, p.85 (Prentice Hall PTR, 1st ed. 2004)
  7. "The mysterious history of the MIT License". opensource.com. opensource.com. Retrieved July 30, 2019. The date? The best single answer is probably 1987. But the complete story is more complicated and even a little mysterious. [...] Precursors from 1985. The X Consortium or X11 License variant from 1987. Or the Expat License from 1998 or 1999.
  8. Hanwell, Marcus D. (January 28, 2014). "Should I use a permissive license? Copyleft? Or something in the middle?". opensource.com. Retrieved May 30, 2015. Permissive licensing simplifies things One reason the business world, and more and more developers [...], favor permissive licenses is in the simplicity of reuse. The license usually only pertains to the source code that is licensed and makes no attempt to infer any conditions upon any other component, and because of this there is no need to define what constitutes a derived work. I have also never seen a license compatibility chart for permissive licenses; it seems that they are all compatible.
  9. "Licence Compatibility and Interoperability". Open-Source Software - Develop, share, and reuse open source software for public administrations. joinup.ec.europa.eu. Archived from the original on June 17, 2015. Retrieved May 30, 2015. The licences for distributing free or open source software (FOSS) are divided in two families: permissive and copyleft. Permissive licences (BSD, MIT, X11, Apache, Zope) are generally compatible and interoperable with most other licences, tolerating to merge, combine or improve the covered code and to re-distribute it under many licences (including non-free or 'proprietary').
  10. "Various Licenses and Comments about Them". Free Software Foundation. Retrieved July 17, 2013.
  11. "Paid software includes MIT licensed library, does that put my app under MIT too?". stackexchange.com. Retrieved July 21, 2021.{{cite web}}: CS1 maint: url-status (link)
  12. "Open Source Licenses in 2020: Trends and Predictions". May 3, 2020. Archived from the original on May 3, 2020. Retrieved May 3, 2020.
  13. Balter, Ben (March 9, 2015). "Open source license usage on GitHub.com". github.com. Retrieved November 21, 2015. 1 MIT 44.69%, 2 Other 15.68%
  14. "MIT License". spdx.org. SPDX Working Group.
  15. "Open Source Initiative OSI – The MIT License:Licensing". Open Source Initiative. Retrieved December 5, 2010.
  16. "MIT License Explained in Plain English - TLDRLegal". tldrlegal.com. Retrieved July 7, 2021.
  17. "X11 License". spdx.org. SPDX Working Group.
  18. "3.3. X Consortium", 3. X/MIT Licenses, The XFree86 Project, March 2004
  19. "X11 License Explained in Plain English - TLDRLegal". tldrlegal.com. Retrieved March 26, 2021.
  20. "General Code License - Fairfield Programming Association". Fairfield Programming Association. Retrieved September 2, 2022.{{cite web}}: CS1 maint: url-status (link)
  21. Chestek, Pamela (August 5, 2020). "[License-review] Request for Legacy Approval of MIT No Attribution License".
  22. "MIT No Attribution". spdx.org. SPDX Working Group.
  23. Langel, Tobie (May 15, 2020). "[License-review] Request for Legacy Approval of MIT No Attribution License".
  24. "FFTW - Fastest Fourier Transform in the West". Massachusetts Institute of Technology. Retrieved July 17, 2020.
  25. Dickey, Thomas E. "Copyrights/comments". Retrieved October 6, 2020.
  26. Dickey, Thomas E. "NCURSES — Frequently Asked Questions (FAQ)".
  27. "Licenses". X.Org Foundation.
  28. "Licensing a repository". GitHub Docs.
  29. "MIT License". ChooseALicense.com. GitHub. September 5, 2022.
  30. "To All Licensees, Distributors of Any Version of BSD". University of California, Berkeley. July 22, 1999. Retrieved November 15, 2006.
  31. "Copyright Policy". OpenBSD. Retrieved June 6, 2016. The ISC copyright is functionally equivalent to a two-term BSD copyright with language removed that is made unnecessary by the Berne convention.
  32. de Raadt, Theo (March 21, 2008). "Re: BSD Documentation License?". openbsd-misc (Mailing list).
  33. "Patents and GPLv3 - FSFE". FSFE - Free Software Foundation Europe. Retrieved December 1, 2020.
  34. "Why so little love for the patent grant in the MIT License?". January 23, 2021. Archived from the original on January 23, 2021. Retrieved January 23, 2021.
  35. "Free and open source software and your patents". May 3, 2020. Archived from the original on May 3, 2020. Retrieved May 3, 2020.
  36. Stern and Allen, Open Source Licensing, p. 495 in Understanding the Intellectual Property License 2013 (Practicing Law Institute 2013)
  37. "The MIT License, Line by Line". May 3, 2020. Archived from the original on May 3, 2020. Retrieved May 3, 2020.
  38. Christian H. Nadan (2009), "Closing the Loophole: Open Source Licensing & the Implied Patent License", The Computer & Internet Lawyer, Aspen Law & Business, 26 (8), 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.
  39. Saltzer, Jerome H (November 18, 2020). "The origin of the "MIT license"". IEEE Annals of the History of Computing. 42 (4): 94–98. doi:10.1109/MAHC.2020.3020234. ISSN 1934-1547.
  40. "Top 20 licenses". Black Duck Software. November 19, 2015. Archived from the original on September 4, 2013. Retrieved November 19, 2015. 1. MIT license 24%, 2. GNU General Public License (GPL) 2.0 23%

Further reading
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