When two or more sound sources radiate identical or nearly identical complex signals, the listener hears a single image located at the nearer source, provided that the delay involved is between about 1 and 50 msec. This phenomenon (together with other closely associated aspects) is generally referred to as the “precedence effect” or “Haas effect.” Less frequently, the terms “law of the first wavefront,” “auditory-suppression effect,” “first-arrival effect,” and “threshold of extinction” have also been used in describing certain of these characteristics. Perhaps the earliest investigator to leave a clear record of his appreciation of the single-image aspect of the phenomenon was Joseph Henry who, in 1849, used the term limit of perceptibility in describing what he had observed. The present paper outlines the historical background of the effect from the standpoint of its investigation and its application in electroacoustical systems.