Access to health care requires both that the population has access in terms of the availability of services and that people take the steps necessary to gain access. Individual behaviours thus form a key determinant of whether and when services are utilised but patient behaviours often do not conform to medical or managerial expectations of appropriate and timely service use. This chapter first examines what have traditionally been regarded as the twin 'problems' ofpatients' delay or non-uptake of services and their inappropriate use of services. It then discusses four types of explanations and models developed to account for these patient behaviours. These are individualistic approaches, social barriers explanations, patient-oriented approaches and a social strategy approach. The chapter concludes with a discusssion of changing policy assumptions and service configurations that place greater emphasis on enabling access through diverse sources to meet patients' needs.