Loïc J. BLUM is Mâitre de Conférences in Biochemistry and Biotechnology at the Université Claude Bernard de Lyon, France. The author or coauthor of some 30 articles and book chapters, he has concentrated on research in immobilized enzymes on membrane supports, heterogeneous enzymology and the role of mass transfer on enzyme kinetics, bioluminescence and chemiluminescence reactions in the heterogeneous phase, and the development of fiber optic biosensors. Dr. Blum received the doctorat de spécialité (1983) in biochemistry and the doctorat d’état ès sciences (1991) from the Université Claude Bernard de Lyon`., PIERRE R. COULET is Professor of Biochemistry and Biotechnology, and head of the enzyme engineering laboratory at the Université Claude Bernard de Lyon, France. From 1974 to 1983 he served as a researcher at the CNRS (National Center for Scientific Research). The author or coauthor of some 100 articles, reviews, and book chapters, he investigates enzyme engineering and biosensors, including heterogeneous enzymology and membrane-bound enzymes, membrane reactors, and amperometric and optical biosensors. He is an editorial board member of the journals Analytical Letters (Marcel Dekker, Inc.), Analusis, and Analytica Chimica Acta. Professor Coulet received the doctorat de spécialité (1973) in chemistry and biochemistry, and the doctorat d’état ès sciences (1978) from the Université Claude Bernard de Lyon.