A parallel glass-plate rotary shearing device has been constructed. This device allows direct observation of the crystallization of polymeric melts being subjected to a constant rate of shear under controlled temperature conditions. Polarized light microscopy and small-angle light-scattering techniques were employed to study the kinetics and morphology of poly(ethylene oxide) melts as they crystallized under various combinations of supercooling and shear rate. The techniques of epimicroscopy, differential scanning calorimetry, and wide-angle x-ray diffraction were used to study the already crystallized material. Crystalline aggregates developing from sheared melts showed a sheaf-like lamellar morphology. The long axes of the sheaf-like structures oriented perpendicular to the flow direction when crystallized under shear. This behavior can be explained in terms of hydrodynamic theory.