In patent law, a “product” or “article” claim covers (well, duh) a product. A “process” claim covers a method of doing something – like making a product. A product claim is infringed by the unauthorized making, using, selling, offering for sale or importing the patented product. A method claim is infringed by the unauthorized practice of the patented process. A third, less well-known, type of patent claim is the “product-by-process” claim which covers a product produced by a particular process¹. What infringes a product-by-process claim?