Drug design refers to a type of inventive process of discovering novel medications based on the understanding of a biological target. Drug repurposing (DR) is the process of identifying new pharmacological indications from existing and old FDA approved drugs. It also uses newly produced drugs for treating conditions that are unrelated to its intended or original therapeutic use. It also entails discovering new therapeutic applications for previously known drugs, comprising abandoned, approved, withdrawn from use and experimental drugs. Traditional drug discovery is a costly, lengthy, risky and difficult procedure. The innovative technique of drug repositioning has the potential to be used instead of traditional drug discovery because it reduces the chance of failure, high financial cost and extended drug development time. There are two basic strategies of DR including on-target and off-target. This book explores all the important aspects of pharmacology and pharmaceutical sciences in the modern day. It covers repurposing techniques and methodologies for drug design. The readers would gain knowledge that would broaden their perspective in this area.