In this chapter, we present the state of the art in trust management systems in mobile ad hoc networks (MANET). First, we consider the rationale for trust management systems by demonstrating the shortcomings of secure routing protocols and incentive-based systems. We then establish the context by exploring the concepts and methodology of traditional trust management systems. In sequent, we analyze and compare recently proposed and few well-reviewed trust management based models for MANET. Finally, we present the limitations and shortcomings of these trust models, and then discuss the possible research directions toward the development of efficient trust management systems.