in american english, the distinction between rental apartments and condominiums is that while rental buildings are owned by a single entity and rented out to many, condominiums are owned individually, while their owners still pay a monthly or yearly fee for building upkeep. condominiums are often leased by their owner as rental apartments. a third alternative, the cooperative apartment building (or "co-op"), acts as a corporation with all of the tenants as shareholders of the building. tenants in cooperative buildings do not own their apartment, but instead own a proportional number of shares of the entire cooperative. as in condominiums, cooperators pay a monthly fee for building upkeep. co-ops are common in cities such as new york, and have gained some popularity in other larger urban areas in the u.s.