Over the past 10 years we have published several papers describing what we call the Energy Cascade approach to crop modeling. We have now incorporated this approach into an interactive PC model that is available for use by other research groups. The model utilizes the primary environmental inputs (temperature, PPF, photoperiod, ’ CO2) along with crop developmental parameters (temperature and photoperiod effects on days to flowering; temperature effect on duration of grain fill) to predict daily canopy carbon gain, yield efficiency (kg per day; kg per mol of photons), and harvest index. The model outputs a series of graphs including a daily carbon gain graph that can be verified by daily gas-exchange data. The model allows for phasic environmental control in which the environmental inputs are changed during the life cycle to improve yield efficiency. Here we describe the principles underlying the model. The effects of sub-optimal environmental conditions will also be examined.