Although biofuels had been used for many years (from 1980 to mid-2007, an estimated 2 trillion miles were driven on ethanol-blended fuels in the United States), it was not until the late 20th and early 21st centuries, with dwindling oil supplies, the threat of global warming, and unrest in the oil-rich Middle East that people began thinking of them seriously as alternatives to petroleum-based fuel. Biofuels were also considered better for the environment than gasoline because they produced far less carbon monoxide, carbon dioxide, sulfur dioxide, and particulate matter, and fewer toxic contaminants, hydrocarbons, and volatile organic compounds. This note describes biofuel production and the many effects its increasing use had on the energy supply, agriculture, and the environment. The use of biofuels was not without controversy, and this note is a good starting point for students who can be asked to research further and identify and discuss the issues presented by biofuel use.