Abstract1.1 Introduction1.2 Growth in Air Transportation, Fuel Use, and CO2 Emissions1.3 Government and Industry Initiatives to Control Air Transportation CO2 Emissions1.4 Transportation System CO2 Intensity1.5 Aircraft CO2 Intensity1.6 Reducing Air Transportation CO2 Intensity1.7 Biofuels for Aviation: Opportunities and Challenges1.8 ConclusionsReferences