There has been remarkable progress during the past decade in understanding of how genetic variations in drug metabolizing enzymes and transporters contribute to observed variation in drug responsiveness. Among drug transporters, the organic anion transporting polypeptide (OATP) class of transporters have proven to be remarkably important to the cellular uptake disposition of a variety of clinically important drugs, particularly in organs such as the intestine and liver; we now know that altered OATP activity may confer reduced efficacy and potentially increased risk of drug-related toxicity. OATP1B1 and OATP1B3 are widely recognized liver-specific members of the family known to modulate the hepatocellular uptake of drugs from the portal vein and thereby modulate systemic exposure and hepatic substrate drug extraction. On the other hand, OATP2B1 and OATP1A2 are expressed on the apical membrane of intestinal enterocytes and though to affect absorption of its drug substrates. Accordingly, genetic variations in these OATP transporters have clinically relevant functional consequences for drug absorption, distribution and excretion, as well as pharmacodynamics response in terms of drug efficacy and toxicity. This article addresses the present evidence of relevance to genetic variations in OATP1B1, OATP1B3, OATP2B1, and OATP1A2 in terms of drug response, efficacy and optimal therapeutics.