In recent years it has become evident that transport processes across membranes play a crucial role in many metabolic systems. The activities of these transport processes often determine the physiology of the organisms.This book presents a state of the art review on the analysis of a wide variety of transport systems from bacteria and eukaryotic cells. A selection has been made of those systems that have been studied at the molecular level with special emphasis paid to the energetic and other biophysical properties. The different classes of transport systems are presented in the following: primary transport, secondary transport, phosphotransferase systems, channels and porines and macromolecular transport. Within each class of transporters several systems are presented by the leading experts in the field, which has resulted in a very broad overview of transport processes in biological cells. In this way the differences in the mechanisms used for translocation become evident while on the other hand features common to the different transport systems are revealed.