Public attention has focused on the depletion of ozone in the upper atmosphere. Experts are also concerned, however, about the formation of ozone pollution in the lower atmosphere, or troposphere, and the resulting threats to human, animal, and plant respiratory health. Most critical to public health is the formation of ozone around large urban areas, where concentrations can be up to three times those considered safe by the U.S. Environmental Protection Agency. This report presents a wide range of current findings on how tropospheric ozone is formed, how well ozone and its precursors are measured, why efforts to date to control the problem have fallen short, what approaches hold the most promise, and what additional research is needed. The recommendations presented in this report provide a roadmap for improving the ozone information base so effective control strategies can be developed.