Key versions of the concept «module» in the sphere of architectural design are considered. Modular structures are defined as a means of creating a flexible and dynamic architectural environment with variable functional parameters, the main potential of which is expressed in the speed of erection, autonomy, economical efficiency, transformative possibilities. The main features and advantages of the modular structures as well as the most effective fields of their application are considered. Examples are given of modular objects from current construction practices that illustrate the possibilities and specific means of their formation. Special emphasis has been placed on the ecological feasibility of modular facilities, as well as on the possibility of their interaction with the established architectural context. The use of the modular method in extreme conditions, including the formation of a habitable environment in outer space, is considered.