Erbium is a rare chemical element. A rare, silvery, white metallic lanthanide, erbium is solid in its normal state. Erbium's principal uses involve its pink-coloured ions, which have optical fluorescent properties particularly useful in certain laser applications. This book reviews research on erbium including synthesis, structural and spectroscopic properties of new erbium-based materials; bismuth-based erbium-doped fibre amplifiers; erbium lasers in the treatment of herpes labialis and for surface conditioning in dentistry, among others.