The reorientation or motion of a defect in a solid can, in favorable cases, be studied by uniaxial stress techniques. The defect is aligned with an applied uniaxial stress at temperatures sufficiently high for the defect to move and then probed with a measurement technique that is sensitive to the defect's orientation. The dynamical properties can be determined by quenching in the alignment and removing the external stress; annealing studies of the disappearance of the stress induced alignment then give a measure of the kinetics of defect motion. Such studies were pioneered by Corbett and Watkins for semiconductor defects and have been performed for a number of centers to provide information about symmetry, diffusion, defect interactions, and internal dynamics. Here, two such studies, the reorientation and diffusion of oxygen in silicon and the motion of hydrogen in hydrogen-containing complexes are described.