This book aims at presenting an overview of the current knowledge of cystatins and molecules of the cystatin superfamily, their structure, physio-and pathological function as well as the direction that research is currently aiming for in developing therapeutic treatments based on cysteine proteinases and related molecules. Its purpose is to give the reader a tool that serves as a reference in the field of protease inhibitor, their physio-and pathological functions and therapeutic potential. It also aims at making accessible to a broader audience, that does not have easy access to scientific publications, a source of knowledge and information. To achieve this goal, the book aims at covering broadly, systematically, concisely, and in depth, the multifacets of the role of cystatins and molecules of the cystatin superfamily in physiopathology, and emphasise on their therapeutic potentials. Figures, self-explanatory schemas and diagrams contribute to clarify and support the data presented.