Open Source Licensing FAQ
This list of Frequently Asked Questions is sponsored by the Open Source Initiative and maintained by a group of community volunteers. It is emphatically not legal advice, nor does it reflect the positions of the OSI Board. Rather, it is merely an evolving compendium of the community's "best shared understanding." If you have additional questions, suggestions, or concerns, please let us know.
Q: How can I choose an Open Source License?
Please visit our License Recommendation page.
Q: Why should I release my source code under an Open Source license?
Because, in many cases, having an active community of contributors helping you improve the software is more valuable (in terms of bug fixes, improved functionality, and customer loyalty) than extracting monopoly rents.
Q: Is it safer for me not to know what patents my open source code might infringe upon?
Q: What does "compatibility" mean in the context of licensing?
Two licenses are typically considered compatible if their terms allow you to create, modify and distribute software that includes code under each license as part of single "work."
In general permissive licenses tend to be compatible with other licenses and restrictive ones do not. For example it is easier to include code from the MIT license in other projects than it is to include code that is licensed under the GPL v2 or later.
Q: Can I freely include code in my project that is under a compatible license?
Not necessarily. Compatibility just means that you can create code that derives from both. However the combined result must respect both sets of copyright terms. Therefore including code under another license may require you to change your own license terms.
In general projects that use a permissive license (such as the MIT license) need to be careful when including other code, but their original code can be widely reused. Conversely projects that use a restrictive license (such as the GPL) can often safely use code from other projects, but their code cannot be reused as widely. This directionality can be a source of conflict between different developers and projects.
Q: What is GPL compatibility?
An important special case of license compatibility is compatibility between the GPL v2 or v3 and anything else. Given the GPL's restrictions on sublicensing, it is usually only compatible with another license when code under the other license can be relicensed under the GPL.
Q: Can I always "relicense" BSD licensed-software under a new license?
If you define relicensing as "sublicensing, possibly under additional terms and conditions which do not contradict the terms and conditions of an original licensor's permissive license", then the answer is generally "yes" -- provided you also retain the original copyright information. However, strictly speaking, you can only modify the license of a "derivative work", and opinions differ on how much change is required to qualify as a derivative work. The MIT license and Academic Free License, for example, freely allow "trivial" sublicensing (without any other changes) as long as the copyright is preserved. Conversely, the Apache 2.0 license only allows sublicensing for "Derivative Works", which it defines as "original works of authorship" -- meaning non-trivial additions. The new BSD license, unfortunately, is silent on this point. If you are planning to "trivially relicense" BSD software, you are encouraged to first check with the copyright holder and/or your own legal counsel.
Q. Are copyleft and other open source licenses, such as the GPL, enforceable under U.S. law?
Open source licensors believe and intend so, or they wouldn't use those licenses for their software. But this question, like many others in open source, hasn't yet been fully tested in a U.S. court. So far, most such cases have been settled rather than tried, so there is very little case law. Of course, such settlements Busybox 1, Busybox 2 themselves may (or may not) indicate that the relevant companies considered it enforceable.
Rather than speculate, if you really need to know the legal consequences of distributing or accepting software under an open source license, we suggest you ask your own lawyer for his or her considered legal opinion.
Q. Is there relevant case law in other countries?
Yes (more details TBD), but generally it is only relevant for the country in question. Judges may choose to look at how other jurisdictions chose to interpret or enforce a particular license for informational purposes, but those decisions don't carry any actual legal weight in, e.g., the U.S. (where most such licenses were originally written).
Q: Can I combine "GPLv2 only" code into a GPLv3 project?
Q: Which version of the BSD licenses should I use?
Q: Can I reuse the Mozilla Public license with my own name and venue?