The assumed global invariance of the constitutive functions of simple lattices produces a certain lack of convexity and the possibility of a wide range of equilibrium configurations. This provides a good model of physics because crystals often prefer complicated morphologies, perhaps at a very fine scale – called microstructures1 – in which various individuals or configurations are present. Microstructures frequently appear in metals and alloys undergoing martensitic phase transitions, the equilibrium arrangements being affected by external loads or changes in temperature. These phenomena are at the basis of such material properties as shape memory, magnetostriction and ferroelectricity, and thus the development of new tecnologies based on these properties rests upon understanding this fine-scale material behavior.