This book deals with the concept of isosterism, bioisosterism and retroisosterism. Specifically it gives the bioisosteric correlation of tetrazole moiety with carboxylic group with the help of different parameters and theories. Carboxylic group is chiefly presents in proteins and peptides, thus emphasis is laid on the fact that how this carboxylic acid has been replaced by the tetrazoles in development of new chemical entities which are under clinical trials and others which are prevailing as drugs in market. Effective results in pharmacokinetic and pharmacodynamic properties of compounds...