Scarce resources are a reality in all health care systems. There is a constant challenge to maximize health benefits within the resources available. This is particularly relevant when caring for critically ill patients, given the resource-intensive technologies and medicines used and the highly specialized professionals required. Moreover, given the high acuity of illness, decision makers and health care providers in critical care units must constantly assess the value derived from therapies and resources used. Economic evaluation is the comparative analysis of alternative health care interventions in their relative costs (resource use) and effectiveness (health effects). Economic evaluations have been increasingly published in critical care journals and read by clinicians. This article illustrates how the basic principles of health economics can be applied to health care decision making through the use of economic evaluation. We demonstrate how economic evaluation can link medical outcomes, quality of life, and costs in a common index, even for therapies for different medical conditions and with different health outcomes. This article highlights the need for randomized clinical trials and economic evaluations of therapies in critical care medicine for which the effect of the therapy on health outcomes and/or costs are unknown.