The federal government has encouraged the development and use of alternative fuels to reduce greenhouse gas emissions associated with aviation and to enhance economic development and energy security for the United States. To help achieve these goals of reducing greenhouse gas emissions, the aviation industry is actively supporting alternative jet fuels. GAO was asked to provide information on the progress and challenges to developing and using alternative jet fuels in the United States. This report examines (1) the role of the federal government in the development and use of alternative jet fuels and (2) key challenges to developing and using alternative jet fuels and actions that the federal government plans to or could take to help address those challenges.