The three classes of US Senators, each currently including 33 or 34 Senators (since Hawaii became the 50th state in 1959, and until another state is admitted), are a means used by the United States Senate for describing the schedules of Senate seats' elections, and of the expiration of the terms of office of the Senators holding the respective seats.

Senatorial classes do not identify who each state's Senior and Junior Senator is - that is determined by comparing the tenures of each state's current Senators, regardless of class.