This chapter serves as a general introduction to psychopharmacogenetics and to the topics covered in this book, which provides the researcher and clinician with an overview of the pivotal topics in psychopharmacogenetics. For much of its history, the focus of pharmacogenetics has been on drug-metabolizing enzymes. This was because of the availability of techniques to detect phenotypic differences between individuals in the plasma level of drugs and to study their genetic basis. The chapter focuses on the methodological issues in pharmacogenetic research design. The interface between psychopharmacology and molecular genetics is already a focus of considerable research activity and this is likely to intensify as anticipated technological advances provide the tools for even more sophisticated studies. It may take longer than originally thought, but ultimately pharmacogenetics and pharmacogenomics will revolutionize the field of clinical psychopharmacology and the development of psychotropic drugs.