Late-stage drug failure can occur due to various factors like unwanted metabolic instability, drug-drug interactions, toxic metabolites, and polymorphic metabolism. To meet the purpose of preventing this failure; sincere effort has been employed by academia as well as the pharmaceutical industry for the development of more effective methods and screening analysis to recognize the metabolic enzymes and profiles involved in drug metabolism. The book elucidates detailed reviews of chosen topics in drug metabolism. The important topics that have been described in this book are: impact of genetic and epigenetic factors on drug metabolism; use of new microdosing methods and new LC/MS and genomic techniques to conclude the metabolic parameters and profiles of potential novel drug candidates; the interaction between metabolism and drug transport in oral biodiversity; and the effect of disease on metabolism and transport.