The interface of ecology and policy is critical in developing approaches for stewardship of Earth’s life support systems. In this session, the process of reviewing air pollution standards for the U.S. based specifically on ecological effects will serve as a unifying case study, and innovative approaches to incorporating scientific data into policy will be discussed. The protection of ecosystems from effects of airborne pollutants presents unique challenges to policymakers, who must consider the most recent scientific evidence and create standards applicable on a national scale across a heterogeneous landscape. Under the 1970 U.S. Clean Air Act, National Ambient Air Quality Standards (NAAQS) were established for ozone, oxides of nitrogen, oxides of sulfur, carbon monoxide, lead, and particulate matter. They include NAAQS for protection against ecological effects which must be reviewed every five years. This symposium focuses on the NAAQS as a real world example of scientific evidence informing policy decisions. In establishing the NAAQS initially, the focus was on gas-phase effects of pollutants. For example, evidence of effects on plant physiology and growth has provided key information in reviewing NAAQS for ozone. Consideration of effects related to deposition of air pollutants has also been incorporated in recent policy assessments. These effects include alteration of physiological and biogeochemical processes, and threats to biodiversity. For example, acidification and nutrient-related effects of aquatic and terrestrial ecosystems from deposition of air pollutants have been the major considerations in the ongoing review of NAAQS for oxides of nitrogen and sulfur (NOx and SOx). This session will begin with an overview of the process for setting NAAQS, including the requirements of the Clean Air Act, key steps in the policy process, review by the public and scientists and the role of the Clean Air Scientific Advisory Committee and the EPA Administrator. A series of presentations will explore how ecological research has informed policy decisions. These presentations will include innovative approaches to developing policies that are ecologically relevant on a national scale while considering local and regional variation in ecosystems and effects, and will feature cutting edge research on effects of ozone on vegetation and on acidification associated with NOx and SOx.