The concept of interface is new to organization theory. What happens when autonomous organizations, within themselves a system, must cooperate with other organizations? Interface is defined as the contact point between relatively autonomous organizations which are interdependent and interacting as they seek to cooperate to achieve some larger system objective. Interface is proposed as a research tool aiding understanding of interorganizational problems. Two organizational systems are examined: a typical aerospace project and an electric power pool. The aerospace industry has made widespread use of a systems management concept which cuts across functional lines. The northeastern power failure of 1965 is used to illustrate failure to apply the interface concept. In the electric power pool, the organization system has lagged behind developments in the technological system. The interface concept is used in analyzing this lag and other possible contributions of this concept are discussed.