Robertson, S. M., Jeffrey, S. R., Unterschultz, J. R. and Boxall, P. C. 2013. Estimating yield response to temperature and identifying critical temperatures for annual crops in the Canadian Prairie region. Can. J. Plant Sci. 93: 1237-1247. Historical yield and temperature data, by municipal district for the three prairie provinces, are used to estimate the marginal effect of exposure to specific temperatures in defined ranges during the growing season. Incorporating these non-linear temperature effects into the model improves yield forecasting for Canadian prairie annual crops over models that use average temperatures or growing degree days. Critical maximum temperatures at which yields decline, calculated for winter wheat, spring wheat, durum wheat, barley, spring rye, fall rye, oats, canola and flax, range between 28 and 34°C, depending on the crop. Additional critical minimum and maximum temperatures are estimated using the marginal effect of exposure to specific temperatures in defined ranges. Estimates of critical maximum temperatures and their marginal impact on yields are important for research and policy analysis on various issues and problems, including climate change, risk management instruments such as crop insurance, and development of heat tolerant crop varieties.