This book provides a self-contained introduction to the field of purification and recycling of metals. It outlines the unifying scientific principles behind the treatment of various metals and discusses the importance of using a clean and properly alloyed metal. The text covers thermodynamics, physical and transport properties, mixing, mass transfer and numerical models. It describes methods for removal of dissolved impurity elements, particles, and inclusions, and considers important aspects of the solidification process, remelting and adding of alloys. Recycling, future challenges and specific processes for each metal are discussed in detail. The book is a greatly extended update of the 1992 book Principles of Metal Refining by T. Abel Engh. It includes, in particular, the subjects of metal recycling, ferrous and non-ferrous metal refining, and metalloids like silicon.