Evidence is needed to inform and guide the choices that healthcare organisations make in relation to how budgets are spent. The associated costs and benefits of health treatments are key components of such decisions. An economic evaluation is a way of systematically identifying the costs and benefits of different health activities and comparing these to make an informed decision about the best course of action based on the evidence available. Economic evaluations can also be used to identify uncertainty around the likely costs of a particular health activity and to compare this against a ‘willingness to pay’ threshold, in order to judge their value for money. This chapter examines the key parts of economic evaluations and the data that feed into them, and considers how the results of economic evaluations can be interpreted.