We have designed and constructed a sealed, temperature‐controlled Couette‐type shear cell which allows us to carry outinsitusynchrotron x‐ray scattering studies of the nonequilibrium structures of complex fluids under flow, probing lengths ranging from the nanometer to the semimacroscopic micron scale. The sealed design allows the cell to be tilted, facilitating the scanning of all directions in reciprocal space. In contrast to existing neutron shear cells, we access the shear plane containing the velocity and the velocity gradient. The temperature control of the cell enables us to carry out phase transition studies far from equilibrium. The complex fluid systems which may be studied with this cell include thermotropic and lyotropic liquid crystals, microemulsions, and polymeric fluids. Recent results on the nematic and smectic‐Aphases of a liquid crystal, and the disordered bicontinuousL3phases of surfactant membranes in the vicinity of the ordered lamellarL&agr;phase under flow, are presented.