The regional nature of several important air pollutants, which include acids, ozone, particulate matter, mercury, and persistent organics (POPs), is widely recognized by researchers and decision makers. Such pollutants are transported regionally over scales from about 100 to a few 1000s of kilometers, large enough to cross state, provincial, national, and even continental boundaries. Managing these regional pollutants requires overcoming political, economic, and cultural differences to establish cooperation between multiple jurisdictions, and it requires recognition of the linkages between pollutants and of impacts at different geographic scales. Here, regional dynamics of the pollutants are discussed, addressing them individually and as a tightly linked physical and chemical system. Collaborative efforts to characterize and manage regional pollution are presented, along with potential directions for future efforts. © 2005 by Annual Reviews. All rights reserved.