GFDL

The GNU Free Documentation License (GFDL) is a copyleft license intended for free documentation and other text-based works. Published by the Free Software Foundation (FSF), it is designed to ensure that users have the freedom to run, study, modify, and distribute the document and any of its derivatives. The license covers manuals, tutorials, help files, and similar content, and is separate from software licenses managed by the FSF.

Core terms of the GFDL require that redistributions and modified versions include the complete text of the license, retain existing authorship attribution, and preserve any included warranty disclaimers and notices. Derivative works may be distributed under the same license or a compatible one. A distinctive and sometimes controversial aspect of the GFDL is the provisions for invariant sections, front-cover texts, and back-cover texts, which may restrict what can be changed in a redistributed document and which must be preserved as part of the publication.

The GFDL has undergone several versions, with the most widely discussed being 1.3. Authors can choose to license works under a specific version or “or any later version” clause, influencing how later updates apply to derivative works. In practice, the GFDL has seen use in a variety of documentation projects, notably in the early documentation of GNU software, but it has also faced compatibility concerns with other free-content licenses, such as Creative Commons licenses. These concerns have contributed to ongoing discussions about license choice for free documentation.