GPL-COMPATIBLE LICENSES

 

Open-source software (OSS) license compatibility is part of each license term which regulates an allowance for the usage of the source code previously released under license A into the new project which has the license B. This means that license A is compatible with license B. Roughly speaking (it is not a strong rule and depends on each license terms), permissive licenses are compatible with protective ones. Vice versa compatibility is usually not the case.

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The GNU General Public License (GPL) is the most popular example of copyleft (protective) licenses. Due to its protective nature, it has a cumulative effect: the amount of software with such license increases every year. As a result, there is often a practical need to use the GPL-released portion of the code as a part of a new or, which is more complex, an existing project already released under a different OSS license. Nevertheless, the flexibility and simplicity of the permissive licenses lead to an increasing trend in their usage over the last years.

 

Care must be taken even during a combination of intellectual property products released under different GPL-family licenses and their versions. The scale from less to more protective GPL licenses is described in the diagram below.