Bile formation is one of the key functions of liver. Hepatocytes are the major cell type in liver and mediate bile formation. Bile salts in portal blood are taken up by hepatocytes with the help of four different transport systems in both a sodium-dependent and sodium-independent manner. The sodium-independent organic anion transporting polypeptides (OATPs), in addition to mediating uptake of bile salts, are important drug transporters. Bile salts are exported from hepatocytes into the canaliculus by the ATP-dependent bile salt export pump (BSEP). BSEP is the only bile salt export system in the canalicular membrane. Its functional impairment, e.g. as a consequence of inhibition by drugs, leads to an intracellular accumulation of bile salts, which are cytotoxic. If BSEP impairment persists, cholestatic liver disease ensues. This chapter gives an overview of the transporters involved in the hepatocellular handling of bile salts. Furthermore, it illustrates the current knowledge on the mechanism of BSEP inhibition by drugs and susceptibility factors leading to drug-induced cholestasis. Finally, it gives an overview on the role of experiments involving transport assays with BSEP during drug development.