Critical in the elimination of drugs and other xenobiotics from the body, cytochrome P450 has strong bearing on scientific assessments of genetic polymorphism in metabolism, possible drug-drug interactions, and bioavailability of candidate drugs. This text systematizes findings on P450 and similar enzymes--as well as parallel issues shaping the pharmaceutical industry--to promote the next generation of safer, more effective drugs. Topics include dioxygen activation, the identification and characterization of metabolites, bioactivation, P450 in lab animal species, enzyme kinetics, reaction phenotyping, drug-drug interactions, pharmacogenetics, hepatic clearance, and the role of UGTs.