Models of health care utilization provide guidance for defining variables, specifying the relationships between them, and evaluating programs and policies concerned with access to and utilization of health care services. This chapter reviews four major types of utilization models: (a) models of patient decision making, grounded in sociological theory and research; (b) the health belief model, based in psychological theory; (c) economic models of the demand for medical care; and (d) the behavioral model of health services utilization that has guided much health services research on access to and utilization of health care services.