This review covers different types of water quality models applied to TMDLs performed to date. It also includes models recommended for@ but not necessarily applied to@ TMDLs. Because there are literally dozens of water quality models@ both public and proprietary@ this review focuses on well-documented models that are in the public domain and most commonly recommended for TMDL use. A range of model complexity is represented in this review. Models that are applicable to a wide range of surface water constituents were evaluated for this study.This report is designed to inform users about the application of models to specific types of TMDL problems@ with emphasis on assuring that predictions of water quality are as reliable and accurate as practical@ given the time and resources available to conduct the TMDL. This review does not recommend any specific model for any particular application.