Silicate glasses are durable solids, and yet they are chemically unstable in contact with aqueous fluids—this has important implications for numerous industrial applications related to the corrosion resistance of glasses1, or the biogeochemical weathering of volcanic glasses in seawater2. The aqueous dissolution of synthetic and natural glasses results in the formation of a hydrated, cation-depleted near-surface alteration zone1, 3, 4, 5, 6, 7, 8 and, depending on alteration conditions, secondary crystalline phases on the surface1, 2, 4, 5, 6, 7. The long-standing accepted model of glass corrosion is based on diffusion-coupled hydration and selective cation release, producing a surface-altered zone2, 5, 6, 7, 8. However, using a combination of advanced atomic-resolution analytical techniques, our data for the first time reveal that the structural and chemical interface between the pristine glass and altered zone is always extremely sharp, with gradients in the nanometre to sub-nanometre range. These findings support a new corrosion mechanism, interfacial dissolution–reprecipitation. Moreover, they also highlight the importance of using analytical methods with very high spatial and mass resolution for deciphering the nanometre-scale processes controlling corrosion. Our findings provide evidence that interfacial dissolution–reprecipitation may be a universal reaction mechanism that controls both silicate glass corrosion and mineral weathering9, 10, 11, 12, 13.