United States patent classification: system organization

Abstract The systematic formulation of the United States patent classification (USPC) is described, starting from the fundamental rationales behind the USPC of utility and structure. The system organization at class and subclass level, as well as topics such as cross-reference art collections and digests in the formation of class schedules are explored in this article, leading to the principles of mandatory and discretionary patent classifications––the basics, the rules and the exceptions.