The book contains basic information about enzyme inhibitors synthesized by microorganisms. Inhibitors having a protein nature, peptides, depsipeptides, oligosaccharides of specific structure and other compounds having inhibitory activity are contemplated. Data on physicochemical properties, specificity, mechanisms of interaction with enzymes, methods of isolation and purification are provided. The focus is on hydrolytic enzyme inhibitors. The question of the function of inhibitors in cultures of microorganisms synthesizing inhibitors, in particular their regulatory role, is discussed. The book is designed for biochemists and microbiologists.