This circular updates a 2004 summary of critical issues in aviation and the environment. The 2005 report identifies priority research that may yield potential benefits to environmental media affected by aviation activities (noise, air quality, and water quality) and processes that link aviation and the environment (analytical tools, environmental review processes, and technology deployment). The individually authored sections of this report define the critical issues in the media or process area; examine the current state of practice, research, and policy; explores a vision of future capabilities that would address the critical issues; and identify specific research needs to help achieve the vision.