This open access book introduces the harmless handling/recycling of magnesium slag , the process of magnesium silicothermic reduction (Pidgeon process)which the slag was produced, and . the magnesium resources, layout of the industry of the world. Examples and experimental data in this book are from the author group's research programs, as well as the rencent researches in China. The book could provide precious reference to scientists and engineers in the field of recycling and environment friendly use of the industrial solid wastes. It could also be used for researchers and students who are interested in relevant field.