The volume is a compendium of the papers and commentaries that were presented at the fourth of a series of four conferences on interpretation of environmental data conducted by the American Statistical Association and the U.S. Environmental Protection Agency. The purpose of these conferences is to provide a forum in which professionals from the academic, private, and public sectors can exchange ideas on statistical problems that confront EPA in its charge to protect the public and the environment through regulation of toxic exposures.The general theme of the papers and associated discussions is the design and interpretation of environmental regulations that incorporate, from the outset, statistically valid compliance verification procedures. Statistical aspects of associated compliance monitoring programs are considered. Collectively the papers deal with a wide variety of environmental concerns including various novel approaches to air emissions regulations and monitoring, spatial sampling of soil, incorporation of potential health effects considerations into the design of monitoring programs, and considerations in the statistical evaluation of analytical laboratory performance.