A simplified organizational diagram of the U.S. EPA illustrates that the Agency is generally organized around its legislative mandate; i.e., media-oriented programs. Since this article focuses on air pollution engineering research, it highlights two of the relevant Assistant Administrator components. The Air and Radiation Office is responsible for setting the agenda for the Agency regarding implementation of air (and radiation) abatement programs, especially implementation of the recently passed Clean Air Act Amendments. The Research and Development Office provides scientific and technical information to support Agency programs. The discussion focuses on air pollution problems and the engineering challenges associated with dealing with them.