The demand for a new edition of this Manual has been enormous. We hope that we have done justice to it and that it will prove a fitting tribute to the late Sam Cowan. He not only obtained every paper he cited in the references but personally perused and annotated each one. We cannot alas say the same. It is now beyond the scope of one person or even of two persons to cover the entire and seemingly everchanging fields of bacterial classification, nomenclature and taxonomy, especially with the range of ‘medical’ bacteria expanding with the advancement of biotechnology and modern medicine to include many environmental organisms. For this third edition we have therefore sought the help of the experts listed on pages xv and xvi for various groups of organisms and we gratefully acknowledge all their contributions to this Manual. The opinions expressed are mostly theirs though the final responsibility is ours. We hope that together they will provide enlightenment and understanding of a subject which, though not everyone's ‘cup of tea’, is nevertheless at the heart of diagnostic medical bacteriology.

In outline, this edition follows that of the two previous ones. We have received numerous suggestions for change but have resisted many of them, preferring to regard continuity as more important.