The Renewable Fuel Standard (RFS) sets annual mandates for renewable transportation fuels sold or introduced into commerce in the United States. The current RFS sets mandates through 2022. The Renewable Identification Number (RIN) system was created by the U.S. Environmental Protection Agency to facilitate compliance with the RFS. A RIN is a 38-character numeric code that corresponds to a volume of renewable fuel produced in or imported into the United States. RINs remain with the renewable fuel through the distribution system and ownership changes. Once the renewable fuel is blended into a motor vehicle fuel, the RIN is no longer required to remain with the renewable fuel. Instead, the RIN may then be separated from the renewable fuel and used for RFS compliance, held for future compliance, or traded. The RFS mandates are prorated down to “obligated parties”—individual gasoline and diesel producers and/or importers—based on their annual production and/or imports. Each year, obligated parties are required to meet their prorated share of the RFS mandates by accumulating RINs, either through fuel blending or by purchasing RINs from others. Understanding the RIN system and the prices for RINs when bought and sold can provide key insights into the impact of mandates on biofuel and feedstock markets. For 2011, conventional ethanol RIN prices have been low, implying low probability that the corresponding mandate has been binding and suggesting that other factors have contributed to expan- sion beyond the mandate. Conversely, biodiesel RIN prices have been high in 2011, implying a more binding biodiesel mandate with effects on soybean oil and other biodiesel feedstock markets.