Gambling is an activity with the following elements: A contract between two or more people, which is based on a forecast of the outcome of an uncertain event involving random processes; Property, referred to as the stake, is transferred between those taking part, so that some gain at the expense of others; The property transfer depends on the outcome or result of the uncertain event, which has been forecast; Participation is voluntary and not necessarily related to gaining the property, but used to obtain an experience. This chapter discusses the clinical features, classification, aetiology and epidemiology, diagnosis, predisposing factors, course and prognosis, management and treatment, and prevention.