Twinning and detwinning in calcite were studied by means of selective etching and sound‐attenuation measurements in order to investigate dislocation behavior during these processes. Twinning was accompanied by an increase in attenuation caused by discontinuous dislocation multiplication in the twin lamella. During detwinning the attenuation changes were recovered by dislocation cluster formation and tangling. It was found that dislocation nucleation accompanies even elastic twinning in calcite and is probably responsible for various anelastic effects associated with it.