William Hewitt studied pharmacy at the University of Nottingham. Later he studied chemistry at the University of London. He worked in the pharmaceutical industry for several years as a quality control analyst; this included the antibiotic sector, where he was introduced to and became fascinated by the microbiological potency testing of antibiotics. This was followed by work overseas as an advisor in quality control of pharmaceuticals. It was overseas that William recognized that the quantitative/mathematical principles of microbiological assay were not well understood. He prepared notes for use in his own laboratory explaining these principles. These were then expanded substantially and published in 1977 by Academic Press as: Microbiological Assay: An Introduction to Quantitative Principles and Evaluation. Few books have been written on the subject of microbiological assay, and the need was perceived for a book with more emphasis on the practical and microbiological aspects of the subject. A second book was produced in 1989, written in collaboration with Stephen Vincent, whose meticulous approach to practical detail and staff training made him an ideal partner. Theory and Application of Microbiological Assay was published by Academic Press. William has been active in promoting the understanding of microbiological assay through technology transfer in several Asian countries. He has also directed several short training courses in the U.K. and the U.S. and has acted as consultant to laboratories in Australia, Belgium, Ireland, Slovenia, and the U.K. Now retired from active laboratory work, William continues to write and produce software for assay evaluation, Hewitt Bioassays. He lives in a delightful rural part of West Wales with his wife and three cats. He has a passion for traditional jazz and plays clarinet.