This chapter focuses on the pharmacokinetic, pharmacodynamic, and pharmacogenomic evidence for black cohosh, echinacea, garlic, ginkgo, ginseng, milk thistle, saw palmetto, and St. John's wort. The fundamental concepts of pharmacokinetics, pharmacodynamics, and pharmacogenomics are provided to assist the interpretation of available evidence. The historical background for each of these eight botanicals is included for context. In addition, results from scientific studies (in vitro and in vivo work) and clinical studies are analyzed to provide our current understanding of the potential impact of botanical-drug interactions when it comes to clinical decision making.