Karst aquifer systems are recognized as some of the most difficult to characterize and model. The multi-porosity structure of interacting matrix, fractures, dissolution features, and layer interfaces and the difficulty in determining the presence and locations of major conduits complicates the modeling of temporal response to recharge and pumping. The variable influence of geologic structure and faults — sometimes acting as conduits, sometimes acting as barriers, sometimes having no effect at all — further complicates model development. Yet, as water supplies become increasingly scarce, resource managers are increasingly relying on groundwater models to assess sustainable yields and to manage spring flows to support critical habitats and surface flows. This session features presentations that illustrate examples of effective aquifer characterization, conceptual model development, computational methods, and approaches for dealing with uncertainties in resource management decisions.