In most patent laws, unity of invention is a formal administrative requirement that must be met by a patent application to become a granted patent. Basically, a patent application can relate only to one invention or a group of closely related inventions. The purpose of this requirement is administrative, as well as financial. That is, the requirement serves to preclude the option of filing one patent application for several inventions, while paying only one set of fees (filing fee, search fee, examination fee, renewal fees, and so on). Unity of invention also makes the classification of patent documents easier.