A high-alloy austenitic CrMnNi steel was deformed at temperatures between 213 K and 473 K (À60°C and 200°C) and the resulting microstructures were investigated. At low temperatures, the deformation was mainly accompanied by the direct martensitic transformation of c-austenite to a¢-martensite (fcc fi bcc), whereas at ambient temperatures, the transformation via emartensite (fcc fi hcp fi bcc) was observed in deformation bands. Deformation twinning of the austenite became the dominant deformation mechanism at 373 K (100°C), whereas the conventional dislocation glide represented the prevailing deformation mode at 473 K (200°C). The change of the deformation mechanisms was attributed to the temperature dependence of both the driving force of the martensitic c fi a¢ transformation and the stacking fault energy of the austenite. The continuous transition between the e-martensite formation and the twinning could be explained by different stacking fault arrangements on every second and on each successive {111} austenite lattice plane, respectively, when the stacking fault energy increased. A continuous transition between the transformation-induced plasticity effect and the twinninginduced plasticity effect was observed with increasing deformation temperature. Whereas the formation of a¢-martensite was mainly responsible for increased work hardening, the stacking fault configurations forming e-martensite and twins induced additional elongation during tensile testing.