Surface acoustic waves (SAWs) are used for a wide variety of signal processing and sensing applications at high frequencies. SAW devices are attractive for these applications because of their small size and low cost relative to many competing technologies. However, SAWs are physically quite different from the acoustic waves encountered in sonar and medical ultrasonics. In addition, the family of surface acoustic waves is quite diverse, with each type of wave having unique electrical and mechanical characteristics. This presentation will describe the physical properties of surface acoustic waves and delineate what distinguishes SAWs from other types of elastic waves. The simple example of an isotropic elastic material will be examined in some detail to illustrate many of the fundamental concepts of SAWs. Methods of generating and detecting SAWs used in device applications will be shown. A simple interdigital SAW device will be described in terms of its composition, design, and electrical and mechanical properties. A brief historical overview on the development of surface acoustic wave devices will also be presented.