The diffraction of a light beam by two orthogonal sound waves is described. The Raman‐Nath equation for the diffracting system is derived and is shown to separate into two Raman‐Nath equations, one for each of the two sound‐wave components. Thus it is shown that diffraction by two orthogonal sound waves present simultaneously in a medium is equivalent to diffraction by the two waves present successively. Analytic solutions of the Raman‐Nath equation are obtained in the Raman‐Nath and Bragg regions of diffraction. Practical applications of the diffraction effect in the Bragg region are outlined.