The rare earths play a unique role in science. These seventeen related elements afford a panoply of subtle variations deriving from the systematic development of their electronic configurations, allowing a test of theory with excellent resolution. In contrast they find widespread use in even the most mundane processes, such as steel-making, for polishing materials and gasoline cracking catalysts. In between are exotic uses such as TV screen phosphors, lasers, high strength permanent magnets and chemical probes. This handbook covers the entire rare earth field in an integrated manner and each chapter is a comprehensive up-to-date, critical review of a particular segment of the field.