P-glycoprotein (P-gp) is a transmembrane protein associated with a phenotype of cross resistance to certain anticancer agents. P-gp is thought to act as an energy dependent pump that expels the anticancer drug out of the tumoral cell, reducing its accumulation and hence its activity. P-gp has been detected in vivo and in vitro in numerous tumor cell types but also in normal tissues and particularly in organs involved in the pharmacokinetic behaviour of xenobiotics. The physiologic functions of P-gp remain unclear but a growing amount of information suggests that it can play an important role at the different steps of pharmacokinetics (i.e., absorption, distribution, elimination). This review gives an update on what is known about the impact of P-gp on the disposition of drugs.