This article introduces the role economics can play in deciding whether programs designed to prevent mental disorders, which carry large disease and economic burdens, are a worthwhile use of limited healthcare resources. Fortunately, preventive interventions for mental disorders exist; however, which interventions should be financed is a common issue facing decision makers, and economic evaluation can provide answers. Unfortunately, existing economic evaluations of preventive interventions have limited applicability to local healthcare contexts. An approach to priority setting largely based on economic techniques— Assessing Cost-Effectiveness (ACE)—has been developed and used in Australia to answer questions regarding the economic credentials of competing interventions. Eleven preventive interventions for mental disorders and suicide, mostly psychological in nature, have been evaluated using this approach, with many meeting the criteria of good value for money. Interventions targeting the prevention of suicide, adult and childhood depression, childhood anxiety, and early psychosis have particular merit.