After a brief review of various applications of ultrasonic techniques, considerable attention is paid to the established methods employed for making sound waves visible. It is shown that these methods are primarily modifications of the technique of ``schlieren photography'' originally developed by Foucault and used frequently for photographing phenomena (e.g., air flow analysis) in which refractive index gradients are set up. The advantages and disadvantages of the various techniques are discussed in some detail and it is shown that a technique employed by Willard is particularly well adapted to the visualization of ultrasonic waves. A modification of this method is discussed, the experimental apparatus is described and typical photographs of ultrasonic wave patterns are shown. In particular, the close analogy existing between light waves and ultrasonic waves with respect to the wave phenomena of refraction, diffraction, and interference is demonstrated in a number of photographs.