John Howard "Jack" Yardley, M.D. (June 7, 1926 - December 7, 2011) was an American pathologist known for his work in gastrointestinal pathology. He worked at Johns Hopkins Hospital from 1954 until his retirement in 2006. He served as Baxley Professor of Pathology and director of the Department of Pathology (a position known as Pathologist-in-Chief) from 1988 to 1992. He also served as associate dean of the Johns Hopkins University School of Medicine from 1977 to 1984. He is regarded as one of the founders of the field of gastrointestinal pathology.