This chapter reviews different approaches to the customer choice behavior model in congested systems from an operations management viewpoint. Considering systems modeled as queues, this chapter particularly focuses on models of individual customer choice rather than on models of aggregate demand with multiple decision-makers in the queueing literature. Factors influencing customer choice behavior are categorized and reviewed in four groups (factors with direct impact on customer utility, customer cognitive ability, customer risk attitude, and information availability), and empirical evidence forming the conceptual framework for studying the proposed factors is provided from the literature. The aim is to convey the point that the performance of a congested system on an aggregate level largely depends on how delay, as the main service/product attribute in such systems, is perceived by the system users in isolation from and in interaction with other attributes. The chapter is concluded by suggestions for future research.