Diffraction of light at 1.15 has been observed from magnetoelastic waves at 1.1 GHz in YIG. A shift in the Bragg diffraction angle was observed when an external magnetic field was varied so as to change the spin wave admixture. The largest shift obtained experimentally was -2.0°, measured from the elastic limit of 9.5°. This shift was accompanied by a delay in the diffracted pulse of about 1 sec. Under quasielastic conditions the diffracted intensity exhibited a series of maxima as the field was swept, due to magnetoelastic Faraday rotation. © 1967 The American Institute of Physics.