In recognition of the increasing trend towards problem orientated learning in medical schools throughout Europe and the USA, the authors felt the need for a problem-based book in medical microbiology to complement the major textbooks in the field. The three authors are each experienced teachers of medical students at the University of London and so have a clear understanding of their requirements. They also have complimentary skills which together cover the entire field of medical microbiology, namely bacteriology, virology and parasitology.