The reduction in the effectiveness of a medication such as antimicrobial or antineoplastic to treat a disease is known as drug resistance. The term is used to denote the resistance that pathogens have acquired. The resistance that a microbe has developed to resist the effects of an antimicrobial medication that could treat it, is known as antimicrobial resistance. Antineoplastic resistance is the resistance of cancerous or neoplastic cells to survive and grow without getting affected by cancer therapies. The microbes acquire resistance to both chemicals as well as physical factors such as temperature, radiation, sound, magnetism or exposure to a chemical. The four mechanisms through which the microorganisms manifest resistance to antimicrobials are the alteration of the target site, drug inactivation and modification, alteration of the metabolic pathways and reduced drug accumulation. This book provides comprehensive insights into the field of drug resistance. It will also provide interesting topics for research which interested readers can take up. The extensive content of this book provides the readers with a thorough understanding of the subject.