Understanding Copyleft

In this FOSSlife Resources section, we previously provided information about the various types of open source software licenses, and, in doing so, we touched on the topic of copyleft. In this article, we’ll look more closely at the meaning and implications of the concept.

Copyleft symbol
Copyleft symbol
(public domain)

The word copyleft is a play on the word copyright, which is a legal term that restricts the use, modification, and distribution of creative works without permission of the owner. Copyleft, among other things, extends the idea of copyright to include derivative works. (Note that the backward C in a circle, shown here, has no legal significance and should not be used to indicate any binding terms.)

Free as in Freedom

The concept of copyleft means making a software program or other work free to use and additionally requiring all modified and extended versions of that program to be free as well. It’s important to note that “free” in this sense refers to freedom – not cost – and you may hear the commonly used phrases “free as in speech” and “free as in beer” used to make this distinction. 

According to the LINFO website, “the origin of the term copyleft is not certain. It may have first appeared in a message contained in Tiny BASIC, a free version of the Basic programming language that was written by Dr. Li Chen Wang in the late 1970s.”

These days, however, the idea is closely associated with the GNU Project, and, according to the GNU website, copyleft includes the following tenets:

  • Copyleft says that anyone who redistributes the software, with or without changes, must pass along the freedom to further copy and change it. 
  • Copyleft guarantees that every user has freedom.
  • Copyleft provides an incentive for other programmers to add to free software. 
  • Copyleft helps programmers who want to contribute improvements to free software get permission to do so. 


The copyleft term is also used to describe certain open source licenses. According to the Open Source Initiative, copyleft “refers to licenses that allow derivative works but require them to use the same license as the original work.” 

As the GNU website notes, “copyleft is a general concept, and you can't use a general concept directly; you can only use a specific implementation of the concept.” Within the GNU Project, the specific implementation and distribution terms are contained in the GNU General Public License (GPL). 

As Joe Casad states in a Linux Magazine article, “The GNU General Public License was born of the simple idea that freedom matters. Yet this simple tool for protecting freedom has another important feature that makes it even more powerful, and that is the ability to build communities.” The amazing growth of projects and communities that make up the open source ecosystem stems in part from this ability to modify and extend tools to meet changing needs.


The freedoms and protections afforded by the principles of copyleft and free and open source software are crucial to developers, users, and communities alike and are key to building sustainable open source software. However, when individuals or companies fail to comply with the stated license requirements, these freedoms are undermined, and compliance can be tricky even with the best of intentions. 

The Software Freedom Conservancy is one organization that helps protect these freedoms through its copyleft compliance work. As the website states, the Conservancy is “dedicated to encouraging all users of software to comply with Free Software licenses.” These efforts are performed collaboratively along with project developers. “All copyright holders involved have the opportunity to give input and guidance on Conservancy's strategy in dealing with compliance issues,” the website states, and the process is further explained here.

The notion of copyleft is powerful, but it’s not perfect. In the words of Eben Moglen, of the Software Freedom Law Center, “copyleft is a great idea that changed the world. It needs refreshment now in order to appeal to a younger generation of people who write programs for sharing. In order to make it appeal to those people who write programs for sharing, we need to make it simpler to use, quicker to understand, and better at doing all the jobs it’s supposed to do.“ Luckily, the concepts inherent in copyleft and free software ensure the ability to continually improve these valuable open source development tools.

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