The effect of shear flow on the structure of multi-component polymer blends and solutions is reviewed. The techniques of small-angle light and neutron scattering, optical microscopy, and fluorescence microscopy are used to directly assess the influence of an externally applied shear field on the phase stability and morphology of model polymer blends and solutions. The polymeric fluids of interest vary from miscible blends and pseudo-binary solutions near a critical point of unmixing to thermodynamically unstable and completely immiscible blends undergoing spinodal decomposition and coarsening in the presence of simple shear flow. We review the influence that critical concentration fluctuations, viscoelasticity, and theological asymmetry have on the shear response of polymer blends and solutions individually, and we discuss the practically important interplay of these three separate effects. We conclude our review by discussing the need for more computational and theoretical efforts focused on shear-induced structure in polymer blends. (c) 2006 Elsevier Ltd. All rights reserved.