The development of recombinant DNA techniques has yielded a large amount of data about the molecular mechanisms of solute translocation across microbial membranes. Kinetic and chemical analysis has also defined many of the properties of the transport proteins involved. It is becoming clear that the transport proteins show many homologies between themselves and with membrane proteins of eucaryotic cells. This book, based on a conference at the royal Society, brings together contributions from many leading workers in the field, presenting common themes and information that have emerged.