Oxide glasses and glass-ceramics comprise a host of materials of widely diverse compositions and properties. It is important to remember that although the properties of a glass or glass-ceramic are intrinsically a function of composition, other factors can often have important, sometimes overriding, effects on observed properties. Such factors include atmospheric weathering and thermal history. Glass-ceramics represent an extreme case because the material, originally a glass, is deliberately heat treated to transform it into a new material whose poly crystalline structure gives rise to a totally different set of properties. This chapter lists out the compositions and properties of glasses and glass-ceramics. For glass-ceramics, the amount and composition of the crystalline and glass phases, as well as the microstructure, have effects that may well substantially alter the intrinsic durability expected on the basis of the overall bulk composition. Strong alkali attack for most silicate glasses and glass-ceramics is quite severe.