Tularemia is a complex clinical disorder caused by the ubiquitous intracellular parasite Francisella tularensis, which has many mammalian and insect hosts. The peak observed incidence of tularemia occurred in 1939, and most present-day clinicians have never seen a case of this disease. Tularemia manifests several different clinical syndromes, depending on the portal of entry. F. tularensis has been used in biological warfare experimentation and it has been weaponized and stockpiled in the past by the United States and other countries. It is classified as a category A critical biological agent by the Centers for Disease Control and Prevention. This article reviews the history, clinical features, diagnostic evaluation, and treatment of this organism with an emphasis placed on its potential role as an agent of biological warfare.