Patentleft is the practice of licensing patents (especially biological patents) for royalty-free use, on the condition that adopters license related improvements they develop under the same terms. Copyleft-style licensors seek "continuous growth of a universally accessible technology commons" from which they, and others, will benefit.^[1][2]

Patentleft is analogous to copyleft, a license that allows distribution of a copyrighted work and derived works, but only under the same or equivalent terms.

Uses

The Biological Innovation for Open Society (BiOS) project implemented a patentleft system to encourage re-contribution and collaborative innovation of their technology. BiOS holds patented technology for transferring genes in plants, and licenses the technology under the terms that, if a license holder improves the gene transfer tool and patents the improvement, then their improvement must be made available to all the other license holders.^[3]

The open patent idea is designed to be practiced by consortia of research-oriented companies^[4] and increasingly by standards bodies. These also commonly use open trademark methods to ensure some compliance with a suite of compatibility tests, e.g. Java, X/Open both of which forbid the use of the mark by the non-compliant.^{[citation needed]}

On October 12, 2001 the Free Software Foundation and Finite State Machine Labs Inc. (FSMLabs) announced a GPL-compliant open-patent license for FSMLabs' software patent, US 5995745 . Titled the Open RTLinux patent license Version 2, it provides for usage of this patent in accordance with the GPL.^[5]