This book delves into the intricacies of N-Nitroso impurities in drug substances, providing a comprehensive overview of their history, formation mechanisms, and risk mitigation strategies. Nitroso impurities, often arising from the interaction of nitrites with secondary or tertiary amines under certain conditions, pose significant safety concerns due to their potential carcinogenicity. The text explores the various pathways through which these impurities are generated during the manufacturing process of pharmaceuticals. It also presents a examination of analytical techniques used to detect nitroso impurities, ensuring compliance with stringent regulatory standards. Furthermore, the book outlines robust strategies to mitigate the risks associated with these impurities, emphasizing the importance of process control, raw material quality, and innovative synthetic methodologies. By addressing these critical aspects, the book aims to enhance the safety and efficacy of drug substances and products, ultimately contributing to improved public health outcomes.