The failure of ceramic structures at elevated temperatures involves the nucleation, growth and coalescence of cavities. The final stage of this process requires the propagation of a crack through the body. Depending on conditions, the fraction of life spent in this crack growth stage may be insignificant, or it may be life limiting. For example, a structure may contain pre-existing flaws either as cracks, or regions of high porosity which readily nucleate cracks. Damage then occurs preferentially in the region surrounding the flaw, and the life of the structure is governed by the rate of crack propagation. On the other hand, if the material is very homogeneous, then cavitation develops uniformly, and it is the nucleation and growth of individual cavity arrays, which govern the life. In real structural ceramics, an intermediate situation is likely to prevail. Large initial flaws can be eliminated by careful processing. However, materials typically contain sufficient inhomogeneity that local regions develop microcracks long before the end of life. These then grow and link until a crack large enough to propagate rapidly across the structure develops. The growth of microcracks may then be the life-limiting process.