The rich variety of fracture behavior exhibited by glasses and ceramic materials is reviewed with particular emphasis on the understanding gained through the use of deliberately introduced, controlled cracks. After a brief summary of the mechanics of indentation cracks four major topics are discussed, the structure of crack tips, environment assisted crack growth, high temperature fracture and the toughening of ceramics. Resolution of the sharp vs blunt crack dilemma is presented together with recent microscopy observations of crack tips in brittle solids. In describing fracture in polycrystalline ceramics we explore some of the complexities beyond the simple Griffith behavior relating strength to flaw size, and show how the scale of the microstructure with respect to the crack length affects the observed toughness. It is shown that the interaction of a crack with the microstructure provides a unifying theme for interpreting much of the current work in the literature and leads to important concepts discussed here, such as the discrete-continuum transition, R-curve behavior, toughening due to crack deflection and crack bridging, transformation toughening and stress-induced microcrack toughening. © 1987.