A formalism in which timing properties of digital hardware may be specified, derived, and formally verified is introduced as a rigorous theory for hardware timing. This approach to reasoning about time differs from current work in that a rigorous modeling framework has been used to create a family of related verification techniques rather than a single timing analysis tool. This framework is based on a model of interacting finite state machines called CIRCAL, a formalism developed for the purpose of describing and validating complex concurrent systems. Its application to digital hardware and the problems associated with timing verification illustrate the utility of a formal approach to hardware description and verification. In this approach to hardware timing analysis, the presence of a composition operator is all pervasive. It provides a single, uniform mechanism for describing the behavior of interacting hardware modules and for establishing and describing the timing properties of such modules. CIRCAL provides us with a proof mechanism for conducting formal hardware verification based on an equivalence relation between CIRCAL terms. This permits the required timing properties of a hardware module to be specified and then formally verified.