With increased computer capacities the continuum-plasticity theory is increasingly important in metal fabrication, forming and performance analysis. State-of-the-art models and their implementations into finite element codes cover material anisotropy and kinematic and distortional hardening. For metals, which are polycrystals, calculations at the crystal length scale are also possible. However, due to computer limitations crystal-plasticity calculations can only be performed for models of very limited size. Nevertheless, crystal-plasticity simulations provide virtual tests, which can be used to calibrate continuum plasticity models, but also to inspire and to develop new and more advanced continuum-scale models. Predictions by crystal-plasticity models differ from continuum models at three strain scales. At small strains, during the elasto-plastic transition, the mix of elastically and plastically loaded grains is of importance for spring-back predictions, the onset of plastic buckling and plastic instabilities. Changes in dislocation structures, occurring during a few percent strain, affect the critical resolved shear stress for glide to occur and gives rise to transients that distort and/or shift the yield surface. Grain rotations take significantly larger strains to occur and results in distortions and rotations of the continuum yield surface.