Studying this book will help one appreciate the molecules called enzymes and the class of enzyme called hydrolases of which proteases make up 70% of. It extensively explains what a cysteine proteases are. It discussed the mechanism of action of cysteine proteases, the uses of cysteine proteases especially plant-sourced cysteine protease and the importance of obtaining such enzyme from Allium cepa (onion). Method of extraction of the enzyme, purification and characterisation were extensively explained. The Results obtained were also discussed and recommendations made. A study of this book will surely help the reader to understand how cysteine protease work, the usefulness of cysteine protease and how to extract, purify and study the properties of the enzyme. The discussion will help the reader understand some of the terms used in explaining the workings of enzymes generally and give one an idea of what one can do with CYSTEINE PROTEASE