The sudden strain increment that results from the unpinning of dislocations or from the activation of dislocation sources can result in observable acoustic emission. A model has been developed that relates the amount of acoustic emission to the size of a dislocation source, the distance the dislocations slip, and to the grain size. The model is able to explain the effect of the microstructure of the metal on the amount of observed acoustic emission. Data obtained on the acoustic emission from various metals support the model. In general, the greatest amount of emission occurs during the application of stress to a test specimen and particularly during yielding. However it is also possible to obtain acoustic emission during removal of a stress in those materials that show a Bauschinger effect.