The connection between resources and readiness is receiving heightened interest at a time when a more austere defense budget and reduced force structures coincide with a range of security challenges. Policymakers and managers want to be sure military expenditures are purchasing the greatest capability possible. Because readiness results from a complex interaction of inputs, policymakers have looked to models as a way of illuminating the connective process. This report identifies, describes, and evaluates how well models currently in use define the connection between resources and readiness. Further, the authors examine how models might fit into the larger context of overall force readiness and how the models might be improved to assess readiness accurately.