The short-range-order structure of lead borate glasses is rather complex and depends on the relative ratios of boron to lead atoms in chemical composition. Different structural groups like penta- and diborates containing three and four coordinated boron, ring- and chain-type metaborate units containing non-bridging oxygens, and boroxol ring can be found in lead borate glasses. Borate glasses with PbO and/or PbX2 content doped with Ln3+ have been investigated using spectroscopic methods in relation to practical applications as solid-state laser active media, NIR tuneable lasers, NIR-to-visible up-conversion systems and broadband optical amplifiers. This new book presents aspects concerning the excited state relaxation of Ln3+ ions in lead borate glasses and glass-ceramics are discussed, as well as optical properties of lanthanide-doped lead borate glasses.