Pertinent information regarding whey-to-fuel ethanol production is explored and reviewed. A potential of producing up to 203 million gallons of fuel ethanol from whey in 2006 was estimated, and dairy cooperatives could have a share of 65 million gallons. Two whey-ethanol plants are currently operated by dairy cooperatives, producing a total of 8 million gallons a year. Successful operations of the plants since the 1980s indicate that (1) fuel ethanol production from whey is technically feasible, (2) whey-tofuel ethanol production technologies and processes are mature and capable of being adopted for commercial operations, and (3) producing fuel ethanol from whey is economically feasible. However, in this era of whey products' price uncertainties, a key consideration in assessing the feasibility of a new whey-ethanol venture should be the valuation of the opportunity cost of whey as feedstock for fermentation. A new wheyethanol plant probably should have an annual production capacity of at least 5 million gallons of ethanol. Some historical lessons on the pitfalls to avoid are summarized.