William Budd (14 September 1811 – 9 January 1880) was an English physician and epidemiologist known for recognizing that infectious diseases were contagious.

He recognized that the "poisons" involved in infectious diseases multiplied in the intestines of the sick, were present in their leaks, and could then be transmitted to the healthy through their consumption of contaminated water.

[2] Using his theory and reading John Snow's essay about cholera in London (1849), Budd took measures to protect Bristol's water supply.

[3] He announced the importance of the work of two Bristol colleagues, Frederick Brittan and Joseph Griffiths Swayne, of organisms (described as "fungoid") in the "rice-water evacuations" of cholera victims.

Part of William Budd's archive is held at the London School of Hygiene & Tropical Medicine.