Discussion to this point in the chapter has largely ignored risk and uncertainty. Crop production is inherently risky and uncertain due to the effects of weather, biological fac­tors including disease and pests, and markets. The actual quantity produced and the price received for a crop may differ considerably from levels expected by the farmer at planting time. Economics of sustainable cellulosic feedstock for biofuels must include considera­tion of risk and uncertainty. Economists distinguish between risk and uncertainty. Risk is defined here as the possibility of two or more outcomes to an action or decision where the probabilities of occurrence of each outcome are known. Uncertainty is defined here as the possibility of two or more outcomes to an action or decision where the probability of each outcome is unknown. The economic implications of risk in crop production are critical to farmer decision making. A failed crop or sharply reduced prices for the crop result in financial losses for the farmer. A series of financial losses may result in financial collapse and loss of the farm business. A cellulosic energy production system is also vulnerable to risk where loss of feedstock supply or adverse variation in prices may bankrupt processors and other businesses in the supply chain.