This study reviews the financial costs of abating greenhouse gas emissions through reducing emissions from deforestation and forest degradation (REDD). It is written from the perspective of an institutional investor seeking cost-effective climate mitigation options. A review of empirical data from Brazil and Indonesia suggests that REDD may, in many areas, provide a cost-effective climate mitigation option, with estimated costs lying in a range of US$ 2-10 per ton of CO2e.