Aviation is an integral part of the global economic and transportation systems. In fact, aviation expansion outpaces the economic growth. Projections indicate that over the next 2 decades, the demand for aviation could grow to about 3 times its present level. This projected growth will likely result in higher aviation emissions and associated impacts on the environment and on human health and welfare, depending upon a variety of factors (such as the size and mix of the operational fleet necessary to meet the stated demand, as well as mitigation steps that could include new technological advances, more efficient operational procedures, market-based options, or regulatory intervention). Nonetheless, it is critical to balance the economic benefits of air travel with environmental concerns associated with this projected aviation growth.