Drug transporters are now increasingly recognized as important determinants of variable drug disposition and response. In addition, transporter associated problems appear to be occurring with greater frequency during the drug discovery and development process. What has not been clear is whether drug transporter related issues are a truly new problem, or whether such issues had existed all along, but were previously unrecognized or ignored. In this review, a brief overview of key drug transporters will be outlined. In addition, a commentary on specific issues of relevance to pharmaceutical sciences in terms of the role and relevance of drug transporters to the drug discovery and development process is provided.