Since the mid 70's there has been a growing concern in the U.S. and Canada about the widespread deposition of acidic materials from the atmosphere. Acid rain is now found over most or all of the northeastern U.S. and southeastern Canada. As they rely more heavily on coal as our major energy source, it is likely that the problem will become more widespread. A major response in both Canada and the U.S. has been the organization of nationwide monitoring programs to assess the geographic and temporal trends in chemical deposition and the initiation of surveys and research efforts to determine current and future impacts on aquatic and terrestrial systems. Both U.S. and Canada monitoring studies show the presence of acid rain in western areas, but at levels several times less acidic than in the east. Surveys based on geological materials and soil types indicate sensitive areas in both countries. Gradual acidification of lakes and streams has seriously affected fish populations in some areas. Leaching of aluminum, heavy metals and plant nutrients from soils affect water quality and may have implications with respect to reduced forest productivity. Extensive programs are underway to determine the extent of potential damage to crops and economic losses. Many other research efforts are underway in both countries to assess both beneficial and detrimental impacts of chemical deposition.