In this paper, we present a hierarchical method that decomposes a system into two subsystems, and restricts the interaction of the subsystems by means of an interface. We present definitions for two types of interfaces [represented as discrete-event systems (DESs)], and define a set of interface consistency properties that can be used to verify if a DES is nonblocking and controllable. Each clause of the definitions can be verified using only one of the two subsystems; thus, the complete system model never needs to be constructed, offering potentially significant savings in computational effort. Additionally, the development of clean interfaces facilitates reuse of the component subsystems. Finally, we examine a simple example to illustrate the method.