Physical property data, rate constants, and equilibrium constants are required for assessments of the fate of chemicals in the environment. Structure-activity relationship (SARs), property correlations, and reactivity correlations arex sources of such data that are increasingly recognized as rapid, practical, and inexpensive methods with which to estimate values of some constants or properties. Although it is unlikely that major environmental decisions will be made based solely on such information, these estimates are often useful within the context of deciding whether better data are required for an assessment, whether a process may be important for a particular chemical, or as a check on a reported value. In some cases, estimated data are useful in concluding that a chemical will or will not persist in a specific environmental situation by simple analogy to experience with other chemicals having similar properties or reactivities. This report reviews a broad range of qualitative and quantitative relationships between structure and properties or reactivities as well as correlations among different properties and reactivities. Also included are the specific theoretical and enpirical equations used in fate assessments that use data produced by these estimation methods. The limitations of these estimation methods are discussed as are testing procedures.