Enormous progress has been made in the field of materials science, it is still many technological challenges, including the development of materials and taking into account the social and environmental impact of their production and use. In this work, the surface treatments of steels are exposed using an accessible and clear terminology. Treatment methods are explained in detail. An example of a plasma nitriding treatment was introduced; this treatment was carried out under different conditions. This book is intended for students and researchers in post graduation.