During the past ten to fifteen years, we have come to realize that transporters, in addition to enzymes, play a vital role in drug elimination. Such insight has been possible because of the continued growth in PK-ADME (pharmacokinetics-absorption-distribution-metabolism-excretion) knowledge, fueled by further advances in molecular biology, greater availability of human tissues, and the development of additional and sophisticated model systems and sensitive assay methods for studying drug metabolism and transport in vitro and in vivo. This has sparked an in-depth probing into mechanisms surrounding DDIs, resulting from ligand-induced changes in nuclear receptors, as well as alterations in transporter and enzyme expression and function. Despite such advances, the in vitro and in vivo study of drug interactions and the integration of various data sets remain challenging. Therefore, it has become apparent that a proceeding that serves to encapsulate current strategies, approaches, methods and applications is necessary. As Editors, we have assembled a number of opinion leaders and asked them to contribute chapters surrounding these issues. Many of these are the original Workshop speakers whereas others had been selected specially to contribute on topics related to basic and applied information that had not been covered in other reference texts on DDI. The resulting tome, entitled Enzyme- and Transporter-Based Drug Interactions: Progress and Future Challenges, comprises of four sections. Twenty-eight chapters covering various topics and perspectives related to the subject of metabolic and transporter-based drug-drug interactions are presented.