Sensitivity analysis strives to answer questions about what data, parameters, model construction choices, and sources of uncertainty are important to predictions. Sensitivity analysis can be conducted using global methods that require 10 to hundreds of model runs per parameter considered. They also can be conducted using local methods that require two runs per parameter considered, but may be limited in their applicability. Less formal methods are also common. This session explores the use of all types of sensitivity analysis methods in models of groundwater systems or integrated hydrologic systems in which groundwater plays an important role. Contributions that address the use of sensitivity analysis to plan data collection and long-term monitoring are encouraged, as well as abstracts which  evaluate the sources of model nonlinearity and their effect on sensitivity analysis and use of sensitivity analysis for sparsely and highly parameterized models.