The concept, especially in U.S. law, that someone who supplied a key thing to allow actual infringement to take place is liable for the infringement. For example, if a patent‘s claims covers a+b+c, someone who supplied c might be liable for infringement. This is limited by the requirement that c be adapted solely or primarily for the infringing purpose, which means that infringement must be the only significant use of c. If c has a substantial non-infringing use, it is deemed a “staple article of commerce” and cannot form the basis of a claim of contributory infringement. See Infringement, Inducement of Infringement.