Copyright is a legal principle embodied in federal law to protect the interests of people who create original works, such as art, literature, film and computer software. Although copyright law was intended to help creative people secure a living from their work, some software designers found that copyright's proprietary restrictions stifled industry creativity. The GNU project is one example of open-source software licensing that encourages widespread innovation using copyrighted materials.
U.S. copyright law gives the creator of an original work the exclusive right to modify, distribute, copy and sell that work for a limited period of years--typically for the life of the creator plus 70 years. Once the copyright period has expired, the work is in the public domain and may be used by anyone. Today's authors may rewrite or publish sequels to 17th century novels, for example, because those works are no longer protected by copyright. Copyright holders can license others to sell or adapt their works if they so choose.
Computer software engineer Richard Stallman began his career at MIT's Artificial Intelligence Lab, where a community of early computer programmers cooperatively developed software that helped drive industry progress. According to Stallman, the culture of sharing that had pervaded early operating system design communities gave way to profit-driven strict copyright enforcement. This approach prevented digital technology users from adapting operating systems and other software to meet their needs. In response, Stallman created the GNU operating system and, as the copyright holder, released it through a General Public License. This license allows, and even encourages, other software engineers to create modifications to the system, provided that those modifications are also released for public use.
The GNU operating system's General Public License works within the context of the copyright law, but adapts that law to best serve the intent of the system's creator. If the GNU operating system designer strictly enforced his copyright, he could prevent all users from making modifications to the software. Had he released the source code for the GNU operating system to the public domain by relinquishing copyright, other software developers could create modifications on which they could claim copyright protection, precluding further free use and development. By the terms of the GNU General Public License, anyone creating modifications to the GNU operating system may do so only if they assign their own copyright interests back to an organization that insures the modified product can also remain freely accessible. The GNU creator refers to this as a 'copyleft' approach. The GNU General Public License now applies to all software created as a derivative of the GNU original source codes.
GNU's General Public License is just one of the many fresh approaches to copyright being used by software designers and other creative individuals. The nonprofit organization Creative Commons has developed a series of licenses that allow artists, composers and other producers of copyrighted materials to license their works for public use while maintaining certain copyright restrictions, such as requiring a notice of attribution. The Open Source Initiative developed from a particular Creative Commons license for software. Software that creators designate as Open Source is licensed for use with terms similar to the GNU General Public License.