Technical Abstract: In cows, the most critical factor influencing the output component of efficiency is reproductive rate, and not necessarily weight gain. Thus benefits of selecting animals with desirable measures of feed efficiency on cow efficiency remain to be determined. The feed input component of cow efficiency in range settings is more complex and subject to greater seasonal and annual variation than in confined settings relying solely on relatively homogeneous harvested feed typical of the grower/finishing phase. Methods to measure feed intake while grazing under range conditions are lacking. Seasonal and annual variations in quantity and quality of forage can result in greater distinctions between biological and economic efficiency in the cow-calf phase compared to other segments. For example, cows that consume more calories during the growing season and gain sufficient weight to exist on less harvested feed inputs during winter may require less total economic input than cows with greater biological efficiency that consume less during the growing season, but require more calories from harvested feed later. While supplemental feed has been relatively inexpensive over the last several decades, changes in demand for feed resources due to increased utilization for bio fuels has resulted in large increases in feed prices. More now than ever, efficiency of beef cattle production will require a balance between economic aspects of nutritional inputs and prolonged optimal output.