The science of sound waves having frequencies above the audible range, that is, above about 20,000 Hz. Original workers in this field adopted the term supersonics. However, this name was also used in the study of airflow for velocities faster than the speed of sound. The present convention is to use the term ultrasonics as defined above. Since there is no marked distinction between the propagation and the uses of sound waves above and below 20,000 Hz, the division is artificial. In this article the emphasis is on instrumentation, engineering applications, analytical uses, and medical applications.