The US Supreme Court recently held that when a licensee files a declaratory judgement against a patentee claiming that its products do not infringe the licensed patent, the patentee bears the burden of proving infringement.  The Supreme Court overruled the Federal Circuit, which had concluded that the licensee plaintiff bore the burden of proof since the patentee defendant was precluded from bringing a patent infringement counterclaim by the existence of the license.  The US Supreme Court opinion can be read Medtronic v Mirowski