This monograph is a comprehensive exploration of the thermochemical treatment of iron alloys, focusing specifically on quenching, carburising, and nitriding. The book introduces the importance of materials engineering in the context of contemporary societal needs and delves into the historical development of thermochemical treatment over the centuries. The global challenges facing thermochemical treatment are also outlined while the three primary development trends identified in the literature at the beginning of the 21st century: reducing thermal deformation in mass production, process modelling, and a multifactorial reduction of treatment costs are also reviewed. Finally, a detailed discussion on the significance of computational methods in advancing thermochemical treatment is included. The book provides a detailed examination of thermochemical treatment processes and their evolution and is a useful tool for graduates, researchers, and professionals working in the area of materials engineering.