The use of ultrasonic techniques for the characterization of microstructural features has attracted much attention in recent years. Although the measurement of ultrasonic parameters has been used for determining material properties for many years, but with the advent of modern signal processing techniques it is possible to extract significantly more information from ultrasonic signals. This has lead to numerous studies being carried out on the effect of microstructures on the propagation of ultrasonic waves and their application to monitoring properties of industrial significance. Examples include the determination of grain size, degree of porosity, amount of second phase particles and measurement of texture and residual stresses. Simultaneously the theoretical models describing the interaction of an ultrasonic wave with these features have been refined.