The Business Source License (BSL, also written BUSL) is a source-available software license developed and promoted by MariaDB Corporation. Its distinguishing feature is a built-in expiration of its own restrictions: code released under the BSL is published with full source from day one and converts automatically to an open source license after a set period. The license text states plainly that “The Business Source License (this document, or the ‘License’) is not an Open Source license. However, the Licensed Work will eventually be made available under an Open Source License, as stated in this License.”
Under the current BSL version 1.1, a licensee is granted the right to copy, modify, create derivative works, redistribute, and make non-production use of the licensed software. Commercial production use beyond the limits set by the licensor requires either a separate commercial license or compliance with an “Additional Use Grant” that the licensor specifies. This lets the author publish the code openly while reserving paid production use, the typical revenue source, for a limited window.
The time-delay mechanism is the heart of the license. The BSL defines a “Change Date,” and the text caps that date at four years after a given version’s first public distribution, whichever comes first. On the Change Date, the rights granted under the restrictive terms terminate and the licensor instead grants rights under a “Change License.” MariaDB’s covenant requires that the Change License be “GPL Version 2.0 or any later version, or a license that is compatible with GPL Version 2.0 or a later version,” guaranteeing that every BSL-covered work eventually becomes genuine open source under GPL-compatible terms.
The BSL was designed to solve a commercial open source dilemma. A company can develop in the open, accept the scrutiny and trust that comes with published source, and still protect a few years of production revenue before competitors, including cloud providers, can freely operate the software at scale. After the Change Date passes, the community inherits a fully open codebase, so the restriction is bounded rather than permanent. This contrasts with permanently restrictive source-available licenses such as the SSPL or the Commons Clause, which never automatically convert.
The BSL has been adopted beyond MariaDB by a number of infrastructure companies seeking the same balance, and it has become one of the canonical reference points in debates about source-available licensing. Its core idea, that openness can be scheduled rather than granted all at once, is an unusual and influential contribution to software licensing: a license that contains, in its own text, the date on which it will stop restricting and start liberating the work it covers.