Ultrasonic instrumentation based on linear and phased array transducers is increasingly being used in clinical diagnosis and yields information not hitherto available. However, the use of ultrasonic arrays is not necessarily restricted to diagnosis. They may, in the future, play an important role in therapy as well. Fundamentals of arrays, current status of systems, and some of the ongoing research on beam shaping by apodization will be briefly reviewed. An attempt will be made to guess at the future based on the current work in various laboratories. [Work supported by NIH.]