In Title IV of the 1990 Clean Air Act Amendments, Congress set out to decrease the adverse effects of acid rain through reductions in annual emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) from utilities burning fossil fuels. The legislation called for placing a cap on utility emissions to achieve a total reduction of 10 million tons of SO2 emissions below 1980 levels by 2010. In combination with reductions under Title I (compliance with National Ambient Air Quality Standards) and Title II (mobile sources), Title IV will contribute to the overall 2-million-ton reduction of Nox emissions from 1980 levels. In contrast to the typical command-and-control approach to regulation, Congress adopted a market-based control strategy for SO2, including an innovative SO2 emission allowance trading and banking program. The Act mandated the interagency National Acid Precipitation Assessment Program (NAPAP) to evaluate the costs, benefits, and effectiveness of Title IV and to assess what further reductions in deposition rates are needed to prevent adverse ecological effects. In compliance, NAPAP conducted its first in a series of quadrennial integrated assessments of Title IV. In this report NAPAP takes a look at the first year of implementation of Title IV by assessing the full causal chain of events, including emission reductions; compliance costs; changes in pollutant concentrations and deposition; effects on aquatic and terrestrial ecosystems; effects on visibility, materials and cultural resources, and human health; and the economic valuation of benefits achieved from reduction emissions.