This book contains, in the form of concise papers of limited length, the proceedings of the 16th ESACT meeting that was held in Lugano, Switzerland, in April 1999. We hope it will become a useful resource of the most up-to-date information in animal cell technology, at least until the next meeting in 2001. Classical approaches for the use of animal cells (for example, production of virus vaccines) remain an important technology. However, it appears that major technological advances and major growth are occurring in other areas. Most importantly, protein production on the basis of recombinant DNA molecules transferred into animal cells appears to be an ever-increasing field of interest and innovation. Increasingly animal cells are being used as substrates for the study of gene activation and repression, and also for the more rapid production of small and moderate quantities of interesting proteins. Tissue engineering, somatic gene/cell therapy, organ-replacement technologies, and cell-based bio-sensors all contribute to a considerable widening of interest and research activity, based on animal cell technology.