Harry Harris was born on 30 September 1919. He was one of the most influential scientists in the field of human genetics during the postwar period in Britain up to 1976, and after that in the United States until his death in July 1994. With his extensive laboratory research on the patterns of human genetic diversity in health and disease, Harris became the acknowledged world leader in human biochemical genetics and assumed the mantle of Archibald Garrod, the founding father. He demonstrated in a series of experiments commenced in 1960, that genetic variation in man (and by implication, other species) was not something rare and unusual and was not always associated with disease. Variation was shown to be commonplace and usually harmless. Harris was also the first to draw attention to the fact that we are all individually different in our genetic constitution and, using simple biochemical tests on isozymes, was able to demonstrate that no two individuals except for identical twins are exactly alike in their genetic make-up. This work prepared the ground for many of the current well known genetic concepts and applied procedures, such as the identification of individuals by DNA ‘fingerprints’ and prenatal diagnosis of genetic disorders. It also led directly to mapping human genes on chromosomes and to the demonstration of considerable allelic heterogeneity in inherited disease. He wrote extensively about his work in research papers and reviews and a series of very influential books (see accompanying Bibliography on microfiche). His first book was An Introduction to Human Biochemical Genetics in 1953 and his last the enlarged 3rd edition of his Principles of Human Biochemical Genetics in 1980. He delivered more than 20 named lectures (see accompanying Bibliography on microfiche) and some of these were also published. Most of his career in the U.K. was centred in London. Following appointments in genetics and in biochemistry at University College, London, and at the London Hospital Medical College, Harris served as Professor and Head of the Department of Biochemistry at King’s College, London, from 1960-65. In 1961 he persuaded the M.R.C. to set up the Human Biochemical Genetics Unit and he was the Honorary Director of this Unit until 1976. In 1965 he was appointed Galton Professor of Genetics and Biometry, back at U.C.L. Then with a final flourish he left England in 1976 to take up the Harnwell Chair in Human Genetics at the University of Pennsylvania, where he worked on a variety of topics until he retired with great reluctance in 1990. Harry Harris was widely honoured and recognized for his major contributions to genetics. He was elected as a Fellow of the Royal Society in 1966, Fellow of the Royal College of Physicians in 1973, Foreign Associate of the National Academy of Sciences, U.S.A. in 1976, Doctor Honoris Causa by the Université René Descartes, Paris in 1976. He also received the William Allen Memorial Award from the American Society of Human Genetics in 1968. Harry Harris had an outstanding career which was devoted to science but sadly shortened by chronic diabetes and he had only a brief glimpse of retirement.