The chemical durability of silicate glasses has long been studied for many applications, in particular when glasses are subjected to environmental weathering and aqueous corrosion. Typical applications include optical instruments, glass vessels, radioactive waste confinement, and bone reparation. Glass corrosion involves ion exchange, water diffusion, network dissolution-recondensation, and secondary phase precipitation. These reactions may impact, among other things, the release of contaminants from waste glasses, and the glass mechanical, optical and catalytic properties. The glass corrosion mechanisms and alteration product formation have been well studied as a function of many environmental parameters (temperature, pH, water composition, etc.). The present chapter describes the general phenomena behind glass corrosion and details glass dissolution in aqueous conditions on one hand and glass vapor hydration on the other hand. The latter phenomenon has not received the same level of attention in the literature relative to the corrosion in aqueous solutions. Research and development needs, in particular in complex systems such as radioactive waste geological repositories, are discussed in the conclusion of the chapter.