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The copyleft logo. It is a copyright symbol (©) mirrored vertically, i.e. one that is opened to the left instead of to the right.

The copyleft is a clause in copyright usage licenses that oblige the licensee to place any processing of the work (e.g. expansion, modification) under the license of the original work. The copyleft clause is intended to prevent modified versions of the work from being passed on with restrictions on use that the original does not have. The copyleft assumes that duplication and processing are permitted in any way. In itself, however, it does not make any further statements about the type and scope of the actual license and can therefore be used in licenses with very different content.

Copyleft originally came up with licenses for free software . There it forces that further developments of a free original program are again free and remain free. It prevents licensees from transferring the program into the proprietary domain through proprietary extensions. In its anti-Linux strategy, Microsoft introduced the critical buzzword virally for copyleft in order to paint the image of a malware that infects all extensions and maliciously kills the possibility of remuneration through license fees, which ultimately threatens the intellectual property of companies . The best known copyleft license is the GNU General Public License (GPL). The same principle was later applied to licenses for free content . Copyleft is not a necessary part of a free software license. For example, the BSD license is not copylefted, but released programs are free software.

Since the licensor himself is not bound to his own copyleft, he can also publish new versions under a proprietary license or allow third parties to do so ( multiple licensing), provided that the licensor is the sole owner of the exclusive rights of use or, if this is not the case, all other rights holders have agreed.


Copyleft is a play on words , the one opposed to the English phrase Copyright (German: Copyright (Engl. "Copy right" means, literally) by replacing "right" right by the opposite, "the left." (English) left ) constructed in which left at the same time the participle of the verb leave (German: "(über) Lassen") is. Analogous to the interchanging of the two terms, the (copyright) situation is also reversed: The right to copy a work is retained even after it has been edited, while it could be restricted by copyright - a trick that copyright uses to protect something achieve what is contrary to its usual purpose. In addition, the copyleft also protects the other freedoms of the respective license after editing the work, e.g. B. with free software free access to the source code .

The term copyleft largely corresponds to the term share alike (sa), which is used in Creative Commons licenses.

The code point U + 1F12F is assigned to the copyleft character ? in the Unicode standard (since version 11.0.0, June 2018).


If an author is allowed to edit the work of another, the editor is given a say in how the edited work may be used, according to current case law. If the original work was still freely copyable, distributable, changeable, etc., these freedoms are not automatically transferred to editing. This is different with copyleft-based licenses: Since the original author also has a say in the edited work, he only allows his share of the work to be passed on if the edits are licensed to everyone with the same extensive rights as in the original license. The copyleft is thus intended to prevent free works from becoming the source material for proprietary content.

The copyleft method was first used by the Free Software Foundation for the GNU licenses ( GPL , LGPL and GFDL ). However, the process is now also used by other organizations. This concerns, for example, various music licenses such as the OAL of the Electronic Frontier Foundation as well as attempts to create a copyleft license that can be used for all types of work, for example the Design Science License (DSL) or the “ShareAlike” licenses of the Creative Commons project (CC-BY -SA and CC-BY-NC-SA, of which the latter does not grant all of the freedoms subsumed under free software due to the restriction to non-commercial use).

Strength of a copyleft

Depending on the degree to which works that contain another work are affected by the license as derivative works, a distinction is made between strong and weak copyleft - the transition being fluid. In the case of a strong copyleft of a piece of music that is used for a film, it can be required that the film itself is also placed under this license, while a weak copyleft would not require this, but only in the event of changes to the piece itself, for example the lyrics.

Historically, this term first emerged with the GPL and LGPL, which are mainly used for software. In particular, program libraries that have been released under a license with a strong copyleft (GPL) may only be linked to programs that are also under the GPL, among other things. The question of how far-reaching a copyleft affects, whether and to what extent it also affects function calls in dynamic libraries or modules loaded at runtime, is partly the interpretation of the license text and therefore partly controversial. In particular, device drivers under proprietary licenses, which are loaded as modules into the Linux kernel under the GPL, often lead to differences of opinion between the respective manufacturer and the kernel developers.

The copyleft of the Mozilla Public License is viewed as very weak, that of the LGPL as weak, and that of the GPL as a strong copyleft (e.g. by the FSF ).


The Open Group and developers of various BSD lines see the prohibition to publish modified versions under a less restrictive license as an inappropriately restricted freedom and advise instead to use free licenses without copyleft (e.g. BSD or MIT license ).

Copyleft licenses can quickly lead to incompatibilities, even with free licenses without copyleft. For example, the original four-clause BSD license , which was later modified accordingly to the three-clause, is incompatible with the GPL, since the license obligation of the four-clause BSD license to mention the author in advertising material, the license prohibition (e.g. in Article 6 of the GPL version 2) to impose restrictions contradicts. Other free licenses for programs are almost exclusively with the GPL dual licensed , d. H. the licensee can choose between the two licenses. Examples of this are the Artistic License (non-copyleft) and the like. a. at Perl and the Mozilla Public License (weak copyleft) at Mozilla, among others . Alternatively, the licenses themselves can allow the work to be placed under another license (e.g. GPL for LGPL Version 2.1) or define themselves as exceptions to an existing license (e.g. LGPL Version 3 Draft 1 as an exception the GPL 3).

Web links

Commons : Copyleft  - collection of images, videos and audio files

Individual evidence

  1. Craig Mundie: Speech Transcript - Craig Mundie, The New York University Stern School of Business. Microsoft, May 3, 2001, accessed November 17, 2019 (speech at New York University Stern School of Business).
  2. ^ Institute for Legal Issues in Free and Open Source Software (ed.): The GPL comments and explains . O'Reilly, 2005, ISBN 3-89721-389-3 , chap. 2 ( online [PDF; 4.8 MB ]).
  3. Dispute over stable driver API for Linux. In: heise online. November 7, 2005, accessed November 17, 2019 .
  4. ^ Richard Stallman : Copyleft: Pragmatic Idealism . In: Free Software Free Society: Selected Essays of Richard M. Stallman . 3. Edition. 2015, p. 188-190 (English, online ).
  5. Mozilla with dual license. In: August 17, 2000, accessed November 17, 2019 . FSF.
  6. GNU Lesser General Public License, FSF, § 3 (English).
  7. GNU Lesser General Public License, 1st discussion draft FSF (English).