Unity of invention

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.

When a patent application is objected to on the ground of a lack of unity, it may be still considered for patent protection, unlike in the case where the invention is found to be lacking novelty. A divisional application can usually be filed for the second invention, and for the further inventions, if any. Alternatively, a patent prosecutor may make a technical argument that there is unity of invention.

Under European patent practice and case law, lack of unity (of invention) can appear either "a priori", before the prior art was examined, or "a posteriori", after the prior art was examined. An a posteriori lack of unity usually results from a lack of novelty or inventive step of the subject-matter of one independent claim.

Under the Patent Cooperation Treaty (PCT), an international application, which is also called PCT application, "shall relate to one invention only or to a group of inventions so linked as to form a single general inventive concept". If the requirement of unity of invention is not met, the International Searching Authority (i.e., the patent office in charge of carrying out the international search) "is entitled to request the applicant to pay an additional search fee for each invention beyond the first which is to be searched".

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Wikipedia