Infectious diseases are transmitted from person to person or from vectors such as mosquitos to people. The uninfected take precautions against these diseases and the infected try to mitigate their symptoms and to get cured. In doing so, people may weigh the costs of illness, prevention and therapy. They may also (altruistically) weigh the costs of people whom their own behavior puts at risk, for instance their sexual partners, or they may act entirely selfishly. Some of these behaviours may therefore lead to externalities and a corresponding rationale for government interventions. A recent literature uses economics to investigate the implications of rational choice by individuals about their response to infectious diseases. It analyzes decisions about prevention, vaccination, testing, therapies and government intervention. This paper reviews this literature with an emphasis on examples from the HIV/AIDS epidemic.