Prediction is the ultimate goal of applied groundwater modeling, and prediction uncertainty is vital to managers. Use of parameter estimation and uncertainty analysis to estimate prediction uncertainty has garnered significant attention in research, large-scale government projects, and the academic realm. This session focuses on integrating parameter estimation and uncertainty analysis into groundwater modeling. This session includes presentations from academia, consulting, research institutes, governmental agencies, and people actively applying parameter estimation and uncertainty analysis to improve groundwater model predictions. Case studies highlighting successful, cost-effective application of uncertainty analysis and parameter estimation to politically, socially, or economically sensitive issues are included.