Anisotropy of crystal structure leads to complications in mechanical behaviour. Robert Cahn, 50 years ago, made valuable contributions through determination of crystallographic features of plastic deformation in large crystals in polycrystalline alpha-uranium. This research area has become increasingly linked with the effects of internal and external stresses on many materials in polycrystalline form comprised of grains with anisotropic crystal structure. The extent of irreversibility of deformation when such materials are subjected to thermal cycles leads to the significance of crystallographic textures but major effects on mechanical behaviour are often apparent where grains are randomly aligned without preferred crystal orientation when small external stresses are imposed. The importance of these features, their main characteristics and their analysis are briefly reviewed (C) 2004 Kluwer Academic Publishers.