Proton-translocating vacuolar ATPases (H+V-ATPase) are increasingly recognized as essential components of most eukaryotic cells. This electrogenic transporter is present in the cell membranes of many differentiated cell types and in the membranes of many subcellular organelles. The primary active pump is a multi-subunit enzyme with a membrane-bound component (V0 domain) and an intracellular catalytic component (V1 domain). The V0 domain is responsible for proton translocation and the V1 domain is responsible for ATP hydrolysis. All the subunits of the H+V-ATPase are now identified and many of their structural and molecular properties are characterized. The H+V-ATPase plays an important role in many physiological processes such as receptor-mediated transport, endocytosis, protein degradation and processing, and intracellular trafficking. In the cell membranes, it contributes to regulation of intracellular pH, secretion of acid, and generation of transmembrane electrical gradients that serve as a driving force for transport across the membrane of these cells. The role of this transporter is perhaps most significant in the kidney where it has been demonstrated in almost all segments of the nephron. H+V-ATPase in the apical membranes contributes significantly to proximal tubule bicarbonate reabsorption and is chiefly responsible for H+ secretion in the distal portions of the nephron. Basolateral H+V-ATPase in other cell types drives luminal HCO3- secretion. Regulation of distal nephron H+V-ATPase is predominantly via shuttling of transporters into and out of the surface membrane.