Yttrium is a silvery-metallic transition metal chemically similar to the lanthanoids and has historically been classified as a rare earth element. The most important use of yttrium is in making phosphors, such as the red ones used in television cathode ray tube displays and in LEDs. Other uses include the production of electrodes, electrolytes, electronic filters, lasers and superconductors; various medical applications; and as traces in various materials to enhance their properties. Yttrium has no known biological role, but exposure to yttrium compounds can cause lung disease in humans. This book presents topical research in the study of Yttrium, including Yttrium in pigments and phosphors; Microwave properties and applications of Yttrium iron garnet films; and the physics and engineering aspects of electronic conduction in Yttrium dihydride.