This chapter highlights the ways in which HIV infection has focused attention on the close relationship between public health practice and the legal system. The chapter begins with a brief summary of the medical aspects of HIV infection, the current data on the scope of infection in Canada and around the world, and an overview of the key public health law debates sparked by HIV. The remaining sections of the chapter will focus on the legal aspects of two major types of public health policies and objectives: case identification and the prevention of transmission.