A critical review of current understanding of the chemical durability of glasses, particularly with regard to mechanisms. Deficiencies in current mathematical treatments are emphasized, in particular, the non-applicability of Fick's laws due to changes in composition and structureof the leached layers. More information on the character of the surface layer is required if outstanding problems are to be resolved. See also AATA (6) F1-83 and 7434. -- AATA