The manuscripts in this section provided an overview of the current status and use of mesocosm studies as they apply to pesticide registration under FIFRA. The chapter discusses the Urban addressed the use of mesocosm studies in OPP/EPA's risk assessment process. It addressed the process for reviewing mesocosm studies submitted to the Agency in support of pesticide registration. Residue data from simulated field studies should be collected in support of the biological effects data. Data on the distribution of residues in the water column and/or sediment are only useful if the biological data are collected from the same spatial compartments. Relative to the most appropriate experimental design, the second study objective outlined in the Guidance Document should be remembered. It is important to provide results for a variety of potential exposure scenarios so risk managers are not restricted in their ability to evaluate the potential impacts under different use scenarios.