To avoid the worst impacts of global warming, we need to make low-carbon biofuels work. But the best biofuels have yet to make the jump from the lab to the pump. As a first step, policy makers should stop spending tax dollars on the dirty biofuels of yesterday and start paying for performance, while maintaining our existing safeguards and standards. But that’s not enough. We need to jumpstart the best biofuels and make them work for our economy and our environment. We need a Billion Gallon Challenge.