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Many groups use the MIT license for their own software, such as expat, MetaKit , XFree86, and (most famously) the X Window System ( X11).

Please note that the term "MIT License", aka "X11 License", is considered ambiguous by the FSF. Quote:

This license is sometimes called the "MIT" license, but that term is misleading, since MIT has used many licenses for software.

1 Text of the license

Copyright (c)

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.

2 Uses of the MIT License

Because the MIT License is not copyrighted, other groups can elect to modify the MIT License to suit their own needs. For example, the Free Software Foundation uses a license identical to the MIT License for its ncurses library, except for the addition of this text:

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.

Adding this text makes it almost identical in its effects to the BSD license.

Still other groups prefer to dual-license their products under the MIT license; an example of this is older versions of the cURL library, which allowed you to choose either the Mozilla Public License or the MIT License.

According to the Free Software Foundation's license list [1], the MIT license is more accurately called the X11 license, because MIT has many licenses for software. However, the Open Source Initiative refers to it as the MIT License, as do most others.

3 Comparison to other licenses

The MIT License is most similar to the 3-clause BSD license, which is essentially different only in the fact that it contains a notice prohibiting the use of the name of the copyright holder in promotion. The 4-clause BSD license also includes a clause requiring all advertising of the software to display a notice; the MIT License has never had this clause. The MIT license, however, more explicitly states the rights given to the end-user, including the right to use, copy, modify, merge, publish, distribute, sublicense, and/or sell the software.

A 2-clause BSD-style license, found in software such as Apple Computer'sApple Computer, Inc. is a Silicon Valley company based in Cupertino, California, whose main business is computer technologies. Best known for its range of Macintosh computers and, more recently, its iPod personal audio ( MP3 and otherwise) player and iTun WebCoreWebCore is a framework developed by Apple, and licensed under the LGPL, to provide an HTML layout engine for Mac OS X. WebCore combines the open source KHTML layout engine developed by the KDE project, with an adapter library called KWQ (pronounced Quack) is, in practicality, the same as the MIT License, as it does not contain the "promotion" clause.