Over the past several decades, groundwater modeling has been used extensively to design and simulate groundwater remediation alternatives, particularly plume capture and pump-and-treat systems. In recent years, models have been increasingly used to design and predict the performance of other remedial technologies, such as permeable reactive barriers, cosolvent/surfactant floods, and injected fluid-based in situ bioremediation approaches. Furthermore, there has been increased understanding that local-scale heterogeneity and aquifer architecture critically affect the performance of these remedies, and that rate-limited diffusion solute exchange between low- and high-permeability zones complicates reagent distribution and significantly influences remedial performance. Consequently, modeling tools and techniques have advanced significantly to simulate more complicated remediation systems and processes, facilitate comparison and optimization of remedial alternatives, and overcome limitations associated with conventional advection-dispersion solute transport approaches.