This thesis studies the fault recovery problem in discrete-event systems using a two-level modular hierarchical approach. We extend the switching modular solutions for failure recovery problems for flat DESs in the framework of Ramadge and Wonham (RW) for supervisory control, using a two-level hierarchical model for DESs. Although in practice, modular design is found to be effective for a variety of systems, in the case of large-scale systems the state sizes may become too large, and so may the computational complexity of these systems for synthesis purposes. Therefore, a hierarchical approach may largely reduce the complexity of practical systems.  We assume that the plant in our problem can be considered as a standard finite-state automaton, describing both normal and faulty behaviors of the system.