William Brown FRS (17 February 1888 – 18 January 1975) was a British mycologist and plant pathologist, known for his ground-breaking research on fungal physiology and the physiology of plant parasitism by fungi, carried out in 1912–28. Born in rural Scotland and educated at the University of Edinburgh, he spent nearly all his career at the Imperial College of Science and Technology in London, where he created the plant pathology research school in the 1920s, becoming Britain's first professor of plant pathology in 1928, and heading the department of botany (1938–53). He was president of the Association of Applied Biologists and the British Mycological Society. He studied Botrytis cinerea, which causes grey mould in a variety of plants, and various Fusarium species that attack apples.