SUMMARYFamous for the discovery of the parasite, Leishmania, named after him, and the invention of Leishman's stain, William Boog Leishman should perhaps be better known for his work in military and public health, particularly the prevention of typhoid. Leishman was a Medical Officer in the British Army from 1887 until his death in 1926. His early research was on diseases affecting troops posted to stations within the British Empire. He saw cases of Leishmaniasis while stationed in India, and was able to identify the causative organism from his detailed records of his observations. Leishman's most important contribution to public health, however, was his work with typhoid, a major cause of morbidity and mortality in the army. Leishman planned experiments and the collection of data to demonstrate the efficacy of anti-typhoid inoculation and, using his considerable political skills, advocated the adoption of the vaccine. He planned for the inoculation of troops in an emergency so, when war broke out in 1914, the vaccine was available to save thousands of lives. Leishman's colleagues and mentors included Ronald Ross and Almroth Wright. Leishman was less outspoken than either Ross or Wright; this paper shows how the different contributions of the three men overlapped.