Endocytosis is a key feature of virtually all eukaryotic cells. It not only provides crucial nutrients to cells but also plays key roles in a cell's interactions with its environment. Roles for endocytosis in immune responses, transcellular transport, signal transduction, neural function and a variety of pathological conditions are now well established. Moreover, studies of endocytic pathways have provided important insights for understanding basic cellular functions associated with membrane trafficking, protein sorting and membrane fusion. In this volume, experts in their respective fields discuss the molecular mechanisms that underlie endocytosis and the fate of endocytic vesicles in cells.