What is the GPL?

The GNU General Public License (GPL) is the most well-known license for "free software."  Version 1 of this license was used for the first time in 1989. The second version of the GPL (→ GNU General Public License, Version 2) appeared in 1991, and the new Version 3 (→ GNU General Public License, Version 3) appeared in 2007. The GPLv2 is essentially the work of Richard Stallman, the founder of the GNU project. Large sections of the Linux kernel as well as numerous other successful Open Source programs are licensed under the GPLv2.
The GPL grants the respective licensee extensive rights to the use of the software: computer programs enjoy copyright protection if they are not completely banal ("Hello World").  Therefore the software can only be used by individuals who are entitled to do so by the rights holder. The rights holder also determines the scope of permitted use.  Under the GPL, the rights holder uses these entitlements to allow everybody to copy, disseminate and make the software publicly accessible license-free and change the software as desired.
For the "freedom to change" to be effective, the licensor also discloses the source code of the software. However, the GPL contains more than rights.  It also involves certain obligations (→ What obligations are involved in distributing software licensed under the GPLv2?). The licensee must take this into consideration when he wants to make use of his rights.  The most important duty in practice is the so-called "copyleft."  This is a clause that obligates anyone who creates and distributes changed versions of the software to subject the changed versions to the GPL and disclose the source code of the modified version.  This ensures that any version of the software derived from the original that is in circulation is under the GPL, and its source code is disclosed.
The GPL is inseparably linked with the Free Software Foundation (FSF). The FSF was founded in 1985 as an organizational and political springboard for supporting free software.  Only the FSF is entitled to publish new versions of the GPL. In addition, it offers extensive information on the GPL (http://www.fsf.org).


This FAQ is based on the FAQs of the commentary “Die GPL kommentiert und erklaert” [Discussions and explanations of the GPL] published by ifrOSS at O’Reilly.
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