By now it ought to be clear that the U.S. must get off oil. We can no longer afford the dangers that our dependence on petroleum poses for our national security, our economic security or our environmental security. Yet civilization is not about to stop moving, and so we must invent a new way to power the world’s transportation fleet. Cellulosic biofuels—liquid fuels made from inedible parts of plants—offer the most environmentally attractive and technologically feasible near-term alternative to oil.