This paper addresses the dependability modeling of ardware and software fault-tolerant systems taking into ccount explicitly the interactions between the various omponents. It presents a framework for modeling these teractions based on Generalized Stochastic Petri Nets GSPNs). The modeling approach is modular: the ehavior of each component and each interaction is epresented by its own GSPN, while the system model is btained by composition of these GSPNs. The omposition rules are defined and formalized through lear identification of the interfaces between the omponent and the dependency nets. In addition to odularity, the formalism brings flexibility and re-sability. This approach is applied to a simple, but still epresentative, example.