Commercial aviation is an extraordinarily complex human venture that has environmental ramifications that are infrequently examined. This chapter presents several ways in which commercial aviation has an environmental impact on the atmosphere. It discusses the procedures and technologies that are candidates for reducing the impacts of commercial aviation on the atmosphere, including greenhouse gas (GHG) emissions and persistent contrails. The National Research Council estimates that domestic air transportation in the US accounts for 7 percent of domestic energy use for transportation, which is in line with the 6 percent of GHG emissions estimated for commercial aviation in the UK. GHG emissions from commercial aviation are only a small fraction of total anthropogenic emissions, but the share of greenhouse gases contributed by aviation is growing rapidly. B. F. Havel and G. S. Sanchez develop ideas about how an international greenhouse gas reduction agreement for commercial aviation might be developed that would require too much space in this setting.