The leishmaniases are a group of diseases with a spectrum of clinical manifestations ranging from self-healing cutaneous ulcers to severe visceral disease and even death. In mammals, the macrophage is the main host for the Leishmania amastigote. However, the macrophage is also the immune effector cell that, upon activation, is able to kill intracellular organisms. Therefore, understanding the parasite mechanisms which allow establishment of infection, and the host immune mechanisms that are responsible for parasite recognition and killing should lead to the development of new drugs and vaccines.