Rare earth elements and rare earth metals are a collection of sixteen chemical elements in the periodic table, namely scandium, yttrium, and fourteen of the fifteen lanthanoids (excluding promethium), which naturally occur on the Earth. The former two are included as they tend to occur with the latter in the same ore deposits. The principal economic sources of rare earth elements are the rare-earth minerals bastnasite, monazite, and loparite and the lateritic ion-adsorption clays. Despite their relative abundance, however, these are more difficult to mine and extract than the sources of transition metals (due in part to their very similar chemical properties), making them relatively expensive. Their industrial use was very limited until efficient separation techniques were developed, such as ion exchange, fractional crystallisation and liquid-liquid extraction. This new book presents the latest research in the field from around the world.