Cysteine, a sulfur-containing amino acid, is vital in preserving the redox potential of cells and is a crucial component of the antioxidant molecule glutathione. Cysteine is involved in numerous vital functions in the body and has been linked to several medical conditions such as cardiovascular disease, neurological disorders, diabetes, cancer, and kidney dysfunction. The objective of this book is to provide a comprehensive summary of the most recent insights on cysteine metabolism and its significance in different pathological conditions.