This paper presents a review of our current understanding of environmentally induced crack growth in glasses, single crystal ceramics, and polycrystalline ceramics. It is shown that the rate of crack growth is controlled by the chemical activity of the active species in the environment as well as by the crack tip stress. A molecular model of a stress-induced chemical reaction between vitreous silica and water is described, and the implications of this model for predicting the effects of other chemical species on crack growth are discussed. Effects of chemical bonding in the solid as well as in the reacting solutions, on the crack growth mechanism are elucidated. Finally, the complicating effects of multigrain arrays on crack extension in polycrystalline ceramics are pointed out.