Open source is celebrating its 20th anniversary, and so is the Apache License. The Apache License is a permissive free software license that is currently in its third iteration. The license allows customers to use intellectual property for any purpose, such as modifying or distributing it.

According to Roman Shaposhnik, member of the Apache Software Foundation board of directors, the license was created from a combination of business interests and a desire of the Apache Group (which later became the Apache Software Foundation) to ensure that the community around Apache httpd web server grew. That Apache web server was actually the first project to be licensed under the Apache License, Shaposhnik said.

“These licenses help us achieve our goal of providing reliable and long-lived software products through collaborative open source software development. In all cases, contributors retain full rights to use their original contributions for any other purpose outside of Apache while providing the ASF and its projects the right to distribute and build upon their work within Apache,” the Apache Software Foundation wrote on their website.

The ASF maintains stewardship over the license. Currently, all Apache Software Foundation projects are required to be under the Apache License, said Shaposhnik.

“Apache License had a huge influence on legitimizing Open Source within the enterprise and business communities,” said Shaposhnik. “While initially GPL made sure that Open Source can survive, it wouldn’t be a stretch to say that Apache License made Open Source thrive.”

The Apache License has gone through three different versions since its creation. Version 1.1 was approved by ASF in 2000, with the primary change from 1.0 being the addition of the advertising clause. The advertising clause specified that derived products were no longer required to include attribution in advertising materials, just in their documentation.

The current version, 2.0, was approved in 2004, with several new goals in mind. With this version, the ASF wanted to reduce the number of frequently asked questions surrounding the license, allow it to be reusable without modification by any project, allow it to be included by reference instead of having to be listed in every file, clarify the submission of contributions, require a patent license on contributions that infringe on the contributor’s own patents, and move comments regarding Apache and other inherited attribution notices to an outside “NOTICE” file, Shaposhnik said.

These changes resulted in the license that is used today, one that is compatible with other open source licenses while still remaining true to the initial goals of the ASF. It also resulted in a license that is supportive of collaborative development across nonprofit and commercial organizations.

The current version has been in place for 14 years, and while there may be business and technology reasons to change it in the future, Shaposhnik compares it to the United States Constitution in that a lot of interests depend on how clearly it can be interpreted and understood.

“With the current version of Apache License we have 14 years worth of foundation to be sure that we understand it pretty well,” Shaposhnik explained. “Any tweak to the license will have to withstand a comparable amount of test of time.”