The physics and technology of acoustooptics are reviewed mainly from the standpoint of designing laser-beam deflection devices and their applications. The ultrasonic light diffraction theory in a form useful for device application is outlined, beginning with the well-known Raman-Nath equation and covering both normal and abnormal types of Bragg reflection. Various acoustooptic materials are evaluated on the basis of two main factors, i.e., acoustooptic figures of merit and acoustic attenuation, as well as availability and optical quality. Guidelines for the selection of materials are discussed in some detail, although they are still insufficient for the complete prediction of new suitable materials. Elements of the acoustooptic light deflector are presented, and the importance of the fabrication techniques is stressed. As examples of the performance characteristics of the deflector, those of TeO2[001] longitudinal-wave and [110] shear-wave deflectors are described. Applications of the deflector to several kinds of apparatus and systems are considered on the basis of the present and the future states of the art.