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* the right to improve the program, and release the improvements to the public. (Access to the source code is a precondition for this)
* the right to improve the program, and release the improvements to the public. (Access to the source code is a precondition for this)
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In contrast, the ''end-user licenses'' that come with proprietary software generally only grant the [[End-user | end-user]] the right to copy the software onto a limited number of computers. The terms and conditions of such license agreements may even attempt to restrict activities normally permitted by copyright laws, such as reverse engineering.
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In contrast, the ''end-user licenses'' that come with proprietary software generally only grant the [[End-user | end-user]] the right to copy the software onto a limited number of computers. The terms and conditions of such license agreements may even attempt to restrict activities normally permitted by copyright laws, such as reverse engineering.
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The primary difference between the GPL and more "permissive" free software licenses such as the ''BSD License'' is that the GPL seeks to ensure that the above points are preserved in copies and in derivative works. It does this using a legal mechanism known as [[copyleft]], invented by Stallman, which requires derivative works of GPL-licensed programs to also be licensed under the GPL. In contrast, BSD-style licenses allow for derivative works to be redistributed as proprietary software.
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The primary difference between the GPL and more "permissive" free software licenses such as the ''BSD License'' is that the GPL seeks to ensure that the above points are preserved in copies and in derivative works. It does this using a legal mechanism known as [[copyleft]], invented by Stallman, which requires derivative works of GPL-licensed programs to also be licensed under the GPL. In contrast, BSD-style licenses allow for derivative works to be redistributed as proprietary software.
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By some measures, the GPL is the single most popular license for [[Free Software|free]] and [[Open Source|open source]] software. As of 2004, the GPL accounted for nearly 75% of the 23,479 free-software projects listed on ''Freshmeat'', and about 68% of the projects listed on ''SourceForge''. (These sites are owned by ''OSTG'', a company that advocates ''Linux'' and the GPL.) Similarly, a 2001 survey of [[Red Hat Linux]] 7.1 found that 50% of the source code was licensed under the GPL, and 1997 survey of [[Metalab]], then the largest free-software archive, showed that the GPL accounted for about half of the licenses used. Prominent free software programs licensed under the GPL include the ''Linux kernel'' and the ''GNU Compiler Collection'' (GCC). Some other prominent free software programs are licensed under multiple licenses, one of which is the GPL; ''Perl'' is a well-known example.
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By some measures, the GPL is the single most popular license for [[Free Software|free]] and [[Open Source|open source]] software. As of 2004, the GPL accounted for nearly 75% of the 23,479 free-software projects listed on ''Freshmeat'', and about 68% of the projects listed on ''SourceForge''. (These sites are owned by ''OSTG'', a company that advocates ''Linux'' and the GPL.) Similarly, a 2001 survey of [[Red Hat Linux]] 7.1 found that 50% of the source code was licensed under the GPL, and 1997 survey of [[Metalab]], then the largest free-software archive, showed that the GPL accounted for about half of the licenses used. Prominent free software programs licensed under the GPL include the ''Linux kernel'' and the ''GNU Compiler Collection'' (GCC). Some other prominent free software programs are licensed under multiple licenses, one of which is the GPL; ''Perl'' is a well-known example.
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===GPL/LGPLv2===
===GPL/LGPLv2===
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By 1990, it was becoming apparent that a less restrictive license would be strategically useful for some software libraries; when version 2 of the GPL was released in June 1991, therefore, a second license - the Library General Public License, or LGPL - was introduced alongside it, and was also numbered version 2 to show that the two were complementary. The version numbers diverged in 1999 when version 2.1 of the LGPL was released, which renamed it the [[Lesser General Public License]] to reflect its place in the GNU philosophy.
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By 1990, it was becoming apparent that a less restrictive license would be strategically useful for some software libraries; when version 2 of the GPL was released in June 1991, therefore, a second license - the Library General Public License, or LGPL - was introduced alongside it, and was also numbered version 2 to show that the two were complementary. The version numbers diverged in 1999 when version 2.1 of the LGPL was released, which renamed it the [[Lesser General Public License]] to reflect its place in the GNU philosophy.
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According to Richard Stallman, the biggest change in GPLv2 was the [[Liberty or Death]] clause, as he calls it - Section 7.<ref name="gplv3conf2stallman-liberty-or-death">[http://fsfeurope.org/projects/gplv3/fisl-rms-transcript.en.html#liberty-or-death Presentation] by Richard Stallman, made on April 21, 2006, at the second international GPLv3 conference, held in Porto Alegre. Direct link to the section about the "Liberty or Death" clause.</ref> This section says that if someone has restrictions imposed that prevent them from distributing GPL-covered software in a way that respects other users' freedom (for example, if a legal ruling states that they can only distribute the software in binary form), they cannot distribute it at all.
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According to Richard Stallman, the biggest change in GPLv2 was the [[Liberty or Death]] clause, as he calls it - Section 7.<ref name="gplv3conf2stallman-liberty-or-death">[http://fsfeurope.org/projects/gplv3/fisl-rms-transcript.en.html#liberty-or-death Presentation] by Richard Stallman, made on April 21, 2006, at the second international GPLv3 conference, held in Porto Alegre. Direct link to the section about the "Liberty or Death" clause.</ref> This section says that if someone has restrictions imposed that prevent them from distributing GPL-covered software in a way that respects other users' freedom (for example, if a legal ruling states that they can only distribute the software in binary form), they cannot distribute it at all.
===GPLv3===
===GPLv3===
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*Additional restrictions
*Additional restrictions
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In January 2006, the [[Free Software Foundation]] began a 12-month public consultation about the possible changes to the GPL. This process is being coordinated by the Free Software Foundation, Software Freedom Law Center, and Free Software Foundation Europe.
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In January 2006, the [[Free Software Foundation]] began a 12-month public consultation about the possible changes to the GPL. This process is being coordinated by the Free Software Foundation, Software Freedom Law Center, and Free Software Foundation Europe.
On July 27, 2006, a [http://gplv3.fsf.org/gpl-draft-2006-07-27.html second discussion draft of GPLv3] was released, along with a first discussion draft of a version 3 of the [[GNU Lesser General Public License|LGPL]].<ref name="gplv3-dd2-released">[http://www.fsf.org/news/gplv3-dd2-released.html Second Discussion Draft of Revised GNU General Public License Released]</ref>
On July 27, 2006, a [http://gplv3.fsf.org/gpl-draft-2006-07-27.html second discussion draft of GPLv3] was released, along with a first discussion draft of a version 3 of the [[GNU Lesser General Public License|LGPL]].<ref name="gplv3-dd2-released">[http://www.fsf.org/news/gplv3-dd2-released.html Second Discussion Draft of Revised GNU General Public License Released]</ref>
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The terms and conditions of the GPL are available to anybody receiving a copy of the GPLed work ("the licensee"). Any licensee who adheres to the terms and conditions is given permission to modify the work, as well as to copy and redistribute the work or any derivative version. The licensee is allowed to charge a fee for this service, or do this free of charge. This latter point distinguishes the GPL from software licenses that prohibit commercial redistribution. Stallman has argued that free software should not place restrictions on commercial use, and the GPL explicitly states that GPLed works may be (re)sold.
The terms and conditions of the GPL are available to anybody receiving a copy of the GPLed work ("the licensee"). Any licensee who adheres to the terms and conditions is given permission to modify the work, as well as to copy and redistribute the work or any derivative version. The licensee is allowed to charge a fee for this service, or do this free of charge. This latter point distinguishes the GPL from software licenses that prohibit commercial redistribution. Stallman has argued that free software should not place restrictions on commercial use, and the GPL explicitly states that GPLed works may be (re)sold.
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The GPL additionally states that a distributor may not impose "further restrictions on the rights granted by the GPL". This forbids e.g. the distribution of the software under a non-disclosure agreement or contract. Distributors under the GPL also grant a license for any of their patents practiced by the software, to practice those patents in GPL software.
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The GPL additionally states that a distributor may not impose "further restrictions on the rights granted by the GPL". This forbids e.g. the distribution of the software under a non-disclosure agreement or contract. Distributors under the GPL also grant a license for any of their patents practiced by the software, to practice those patents in GPL software.
Section three of the license requires that programmes distributed as pre-compiled binaries are accompanied by a copy of the source code, a written offer to distribute the source code via the same mechanism as the pre-compiled binary or the written offer to obtain the source code that you got when you received the pre-compiled binary under the GPL.
Section three of the license requires that programmes distributed as pre-compiled binaries are accompanied by a copy of the source code, a written offer to distribute the source code via the same mechanism as the pre-compiled binary or the written offer to obtain the source code that you got when you received the pre-compiled binary under the GPL.
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The GPL does not give the licensee unlimited redistribution rights. The right to redistribute is granted only if the licensee includes the [[source code]] (or a legally-binding offer to provide the source code), including any modifications made. Furthermore, the distributed copies, including the modifications, must also be licensed under the terms of the GPL.
The GPL does not give the licensee unlimited redistribution rights. The right to redistribute is granted only if the licensee includes the [[source code]] (or a legally-binding offer to provide the source code), including any modifications made. Furthermore, the distributed copies, including the modifications, must also be licensed under the terms of the GPL.
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This requirement is known as [[copyleft]], and it gets its legal teeth from the fact that the program is copyrighted. Because it is copyrighted, a licensee has no right to modify or redistribute it (barring [[fair use]]), except under the terms of the copyleft. One is only required to adhere to the terms of the GPL if one wishes to exercise rights normally restricted by copyright law, such as redistribution. Conversely, if one distributes copies of the work without abiding by the terms of the GPL (for instance, by keeping the source code secret), they can be sued by the original author under copyright law.
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This requirement is known as [[copyleft]], and it gets its legal teeth from the fact that the program is copyrighted. Because it is copyrighted, a licensee has no right to modify or redistribute it (barring [[fair use]]), except under the terms of the copyleft. One is only required to adhere to the terms of the GPL if one wishes to exercise rights normally restricted by copyright law, such as redistribution. Conversely, if one distributes copies of the work without abiding by the terms of the GPL (for instance, by keeping the source code secret), they can be sued by the original author under copyright law.
The copyleft thus uses copyright law to accomplish the opposite of its usual purpose: instead of imposing restrictions, it grants rights to other people, in a way that ensures the rights cannot subsequently be taken away. This is the reason the GPL has been described as a "copyright hack". It also ensures that unlimited redistribution rights are not granted, should any legal flaw (or "computer bug") be found in the copyleft statement.
The copyleft thus uses copyright law to accomplish the opposite of its usual purpose: instead of imposing restrictions, it grants rights to other people, in a way that ensures the rights cannot subsequently be taken away. This is the reason the GPL has been described as a "copyright hack". It also ensures that unlimited redistribution rights are not granted, should any legal flaw (or "computer bug") be found in the copyleft statement.
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The GPL was designed as a license, rather than a contract. In some Common Law jurisdictions, the legal distinction between a license and a contract is an important one: contracts are enforceable by contract law, whereas the GPL, as a license, is enforced under the terms of copyright law. However, this distinction is not useful in the many jurisdictions where there are no differences between contracts and licences, such as Civil Law systems.
The GPL was designed as a license, rather than a contract. In some Common Law jurisdictions, the legal distinction between a license and a contract is an important one: contracts are enforceable by contract law, whereas the GPL, as a license, is enforced under the terms of copyright law. However, this distinction is not useful in the many jurisdictions where there are no differences between contracts and licences, such as Civil Law systems.
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The way the GPL license works is simple: if you do not abide by the GPL's terms and conditions, then you do not have permission, under copyright law, to copy or distribute GPL licensed software or derivative works. It does ''not'' mean that the rules of the GPL do not apply to you and that you may use the software however you like. By default, the restrictions of copyright law are in effect, not the anarchy of the public domain.
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The way the GPL license works is simple: if you do not abide by the GPL's terms and conditions, then you do not have permission, under copyright law, to copy or distribute GPL licensed software or derivative works. It does ''not'' mean that the rules of the GPL do not apply to you and that you may use the software however you like. By default, the restrictions of copyright law are in effect, not the anarchy of the public domain.
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*[http://www.gnu.org/philosophy/enforcing-gpl.html Enforcing the GNU GPL] by Eben Moglen, September 10, 2001
*[http://www.gnu.org/philosophy/enforcing-gpl.html Enforcing the GNU GPL] by Eben Moglen, September 10, 2001
*[http://www.groklaw.net/staticpages/index.php?page=20050131065655645 Groklaw GPL References]
*[http://www.groklaw.net/staticpages/index.php?page=20050131065655645 Groklaw GPL References]
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*[http://www.rattlesnake.com/software-law/GNU-GPL-and-Commentaries.html GNU General Public License and Commentaries] - Edited by [[Robert Chassell]].
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*[http://www.rattlesnake.com/software-law/GNU-GPL-and-Commentaries.html GNU General Public License and Commentaries] - Edited by [[Robert Chassell]].
*[http://www.dwheeler.com/essays/gpl-compatible.html Make Your Open Source Software GPL-Compatible. Or Else.] (David A. Wheeler, [[7 April]] [[2004]]) — why a GPL-compatible license is important to the health of a project
*[http://www.dwheeler.com/essays/gpl-compatible.html Make Your Open Source Software GPL-Compatible. Or Else.] (David A. Wheeler, [[7 April]] [[2004]]) — why a GPL-compatible license is important to the health of a project
*[http://software.newsforge.com/software/04/07/15/163208.shtml "Toward True Open Source"] - an article about why the GPL is allegedly too restrictive
*[http://software.newsforge.com/software/04/07/15/163208.shtml "Toward True Open Source"] - an article about why the GPL is allegedly too restrictive
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**[http://fsfeurope.org/projects/gplv3/barcelona-rms-transcript.en.html A transcript of Richard Stallman's presentation]
**[http://fsfeurope.org/projects/gplv3/barcelona-rms-transcript.en.html A transcript of Richard Stallman's presentation]
**[http://fsfeurope.org/projects/gplv3/barcelona-moglen-transcript.en.html A transcript of Eben Moglen's presentation]
**[http://fsfeurope.org/projects/gplv3/barcelona-moglen-transcript.en.html A transcript of Eben Moglen's presentation]
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[[Category:Concepts & Terms]]
[[Category:Concepts & Terms]]
[[Category:Open Source]]
[[Category:Open Source]]