In order to predict with some degree of certainty whether any test method can be adapted to a particular inspection problem or more fundamentally to develop methods which can be applied, the physical principles of methods must be understood as completely as possible. Only after such an understanding has been obtained can further exploitation and technical development along particular Unes be justified. The general inadequacy of available methods for the inspection of metals at war-time production rates was first indicated by experience during World War II. The realization of this situation came too late, however, to allow for revision of methods then used and the substitution of new ideas for inspection tests. In a few specialized cases, new methods were provided and adopted, but these methods were by no means fully exploited. A test method which aroused considerable interest during the war, utilizes energy in the form of high frequency vibrations (ultrasonic vibrations) for the detection of flaws in certain parts. Successful application of this method in specific cases indicated a much wider utilization of the principles employed therein. The report presented herewith is a summary of available technical literature through 1946 on the subject of ultrasonics as applied to metals. Particular emphasis has been placed on the detection of flaws or discontinuities in metals since the bulk of the literature encountered has dealt with this application. However, other metallurgical applications were encountered and have been included for the sake of completeness and to promote speculation along these lines.