|Licensing of patents|
|Clauses in patent licenses|
Patentleft (also patent left, copyleft-style patent license) 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.
Uses of patentleft
The Biological Innovation for Open Society (BIOS) project implemented a patentleft system to encourage re-contribution and collaborative innovation of their technology. BIOS holds a 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. 
Person A has a patent, and licenses it under a patentleft license.
Person B has two patents in her product and wants to use Person A's patents in that product. Person B also wants to charge royalties for her two patents. She decides to use Person A's patent, but now must license her patents, royalty-free, under the same terms as Person A's patent.
Person C has three patents in his product and wants to use Person B's two patents in that product, but doesn't want to use Person A's patent. Person C also wants to charge royalties for his three patents. He decides to use Person B's patent, but now must license his patents, royalty-free, under the same terms as Person A's patent.
- Ménage, Guillaume; Dietrich, Yann (March 2010). "“Patent Left”". Les Nouvelles (Licensing Executives Society International): 42–46. Archived from the original on 2011-07-16. Retrieved 2010-11-30.
- Richard Stallman (1999-06-22). "On "Free Hardware"". — Richard Stallman criticizes patentleft because of cost of applying for patents
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