Zwambag, A., Kelly, M., Schenkel, F., Mandell, I., Wilton, J. and Miller, S. 2013. Heritability of beef tenderness at different aging times and across breed comparisons. Can. J. Anim. Sci. 93: 307-312. The heritability of shear force at 7, 14 and 21 d was estimated from a crossbred population of beef cattle. The population consisted of approximately 1400 crossbred cattle that were predominantly the offspring of Angus, Simmental, Gelbvieh and Piedmontese sires bred to predominantly Angus and Simmental females. Significant breed effects on tenderness were found within each aging time and no effect of heterosis was detected. The heritability of shear force declined from 0.194 to 0.048 as aging time increased from 7 to 21 d, highlighting the effectiveness of aging as a tool to improve tenderness. The repeatability of shear force was also found to be moderate (0.53). However, as energy prices increase it may be attractive to reduce aging times, thus breeding animals that are more tender at shorter aging times would be beneficial. The heritability of tenderness found at shorter aging times would indicate that improvement in this trait would be possible within a population where phenotypes are available.