This chapter discusses the evidence for a heritable component to psychotropic drug response. It reviews basic methodological issues in pharmacogenetic studies of psychotropic drug response, and highlights future directions for pharmacogenetics research in psychiatry. The majority of heritability data on psychotropic drugs is from studies of antidepressant drug response. Antipsychotic drugs are potent dopamine receptor antagonists. Many of the single nucleotide polymorphisms (SNPs) that are being identified may be useful in pharmacogenetic studies. The considerable advantages of the case-control approach for pharmacogenetic studies, coupled with the genomic control methods, suggest that it should be feasible to conduct large-scale pharmacogenetic studies with increased power and with decreased potential for undetected ethnic stratification. The first generation of pharmacogenetic studies that utilized SNPs in relatively limited numbers of candidate genes will be replaced by pharmacogenomic studies in which the complete genome is assessed.