This book concerns the design, operation and application of devices capable of generating acoustic waves in the ultrasonic frequency range. It emphasizes the study of chemical and/or biochemical systems imposed on the surface of such devices, whether operated in the gas- or liquid-phase, i.e. on acoustic wave chemical and biological sensors. It focuses on devices that employ acoustic waves launched and received on the same surface. It touches upon such diverse areas as acoustic wave physics, applied mathematics, chemistry, electronics, fluid mechanics, materials science and polymer science.