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With the increased use of acoustic emission as a nondestructive testing tool, it has become extremely important to document and to understand the emissions characteristic of various modes of deformation and fracture. In the present work, results are reported of acoustic emission measurements made during mechanical deformation of indium single crystals. Although the metal indium is of little structural importance, it develops well‐delineated twins with associated acoustic emissions, and therefore affords an excellent medium with which to develop techniques and to generate interpretations which can be applied to structurally important materials. By recording the acoustic emission signals on a video‐tape recorder it was possible to play them back as often as desired and to observe them in slow and stop motion. The experimental results show that a correspondence exists between the duration of the acoustic signal and the volume of twinned material as determined by cinematographic observation of the generation and growth of twin bands. Repetition of some waveform features was demonstrated not to be the result of multiple reflections of the emitted elastic waves from bounding surfaces, but to be related to actual physical events associated with the twinning process. It was also demonstrated that the direction of the stress, tensile, or compressive, induced in the body of the crystal due to twinning, can be determined from the polarity of the elastic wave emitted by the twin as detected by the transducer.