In May 2015, EPA released its delayed revisions to the Renewable Fuel Standard (RFS) for 2014 and beyond. This standard establishes volumetric requirements for total renewable fuels and several subcategories of advanced biofuels. With the current rulemaking, EPA is attempting to revise its standard-setting process as the practical realities of the transportation fuel market have caught up with many of the program’s more ambitious policy aspirations. Regardless of how the rulemaking plays out, policymakers will need to decide whether EPA is best positioned to take the lead in reinterpreting those aspirations, or whether Congress should step back in.