Decision-making, the selection of a choice among alternatives, is of critical importance in EMS. EMS are provided, under great time pressure, with many concurrent, high-stakes activities occurring simultaneously in a high-technology environment of practitioners (either providing care or operating an ambulance), dispatchers, and patients all affecting the outcome. In this environment, patient outcomes depend on timely and accurate human decision-making. Improving the decision-making of highly trained and high-performing professionals is a difficult challenge. In this chapter, we argue that decision-making in EMS can be improved through interventions targeting the immediate precursors of good decision-making. Situation 28awareness (SA), the degree to which one has actionable, goal-directed knowledge (Rousseau et al., 2004) of elements in the prehospital environment, provides a metric of precursors of effective decision-making in EMS.