GLOSSARY / LICENSE TERMS
What is license compatibility?
License compatibility is whether two or more software licenses allow their code to be combined and distributed in one work. This glossary entry defines it plainly for enterprises and explains why the relicensing wave has turned a once stable check into a live risk.
Definition
License compatibility describes whether the terms of two or more licenses can be satisfied at the same time in a single combined and distributed work. Two licenses are compatible when you can comply with both at once. They are incompatible when one requires something the other forbids, so no single distribution can meet both sets of conditions. Compatibility is a property of the combination, not of either license alone. A license that is permissive and accommodating on its own can still produce an incompatible result when paired with a license that pulls in the opposite direction.
How compatibility actually arises
Permissive licenses such as the MIT license and Apache License 2.0 impose few conditions, so they combine cleanly with most other licenses, and the combined work simply carries the stricter terms of whatever it is paired with. Copyleft licenses such as the GNU GPL and the GNU AGPL are more demanding, because they require derivative works to carry the same terms, which can reach into code combined with them. Incompatibility tends to appear when two licenses each impose conditions the other cannot meet, or when an open source license is combined with a source available license that adds use restrictions an open license never contemplated. The practical test is always the same: can one distribution satisfy every license at once.
Why license compatibility matters to enterprises
A single incompatible component can make a product impossible to ship lawfully under its current terms. If a strong copyleft obligation reaches your proprietary code, or a source available restriction conflicts with the license of the code beside it, the result is software you built but cannot distribute the way you intended. For an enterprise shipping products or operating services, that is a release blocker and a commercial exposure at once. Compatibility belongs in the same conversation as the rest of your license posture, which we set out in relicensing and license compatibility conflicts.
Why it matters after the relicensing wave
Compatibility used to feel like a one time check made when a component was adopted. The relicensing wave changed that. When a project moves to the Business Source License or the Server Side Public License, the new terms add restrictions that may conflict with the licenses of the code it sits beside, as of the version that carries the change. A combination that was compatible under the old open license can become a compliance problem under the new one, even though your own code never moved. Source available is not open source, and the added restrictions are precisely what can break a combination that used to hold. Knowing which components have relicensed, and where they sit in your tree, is the basis of a clean answer, which we cover in source available is not open source and why it matters.
For more definitions, see the full open source license glossary.
COMMON QUESTIONS
Questions buyers ask.
What is license compatibility?
License compatibility is whether two or more software licenses allow their code to be combined and distributed together in one work. Two licenses are compatible when you can satisfy the terms of both at the same time. They are incompatible when one license demands something the other forbids, so no single distribution can comply with both.
Why does license compatibility matter to enterprises?
Because a single incompatible component can make a product impossible to distribute lawfully under its current terms. Combining a strong copyleft license such as the GNU GPL with a license that adds incompatible restrictions can leave you unable to ship the result. After the relicensing wave, components that were compatible when adopted may no longer be, which is why compatibility is a live risk rather than a one time check.
Can a permissive license be incompatible with copyleft?
Permissive licenses such as MIT and Apache License 2.0 are usually compatible with copyleft licenses because they impose few conditions. The combined work simply carries the stronger copyleft terms. Incompatibility more often arises between two licenses that each impose conditions the other cannot meet, or between an open source license and a source available license that adds use restrictions.
How does relicensing affect license compatibility?
A relicense can turn a compatible component into an incompatible one. When a project moves to the Business Source License or the Server Side Public License, the new terms add restrictions that may conflict with the licenses of the code it sits beside. Software that combined cleanly under the old license can become a compliance problem under the new one, even though your own code did not change.
Is this legal advice about license compatibility?
No. This is a commercial and licensing risk reference, not legal advice. Whether two specific licenses are compatible for your particular combination and distribution is a question for your own counsel.
ASSESSMENT
Know which licenses govern your stack.
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