The United Nations climate negotiations on reducing emissions from deforestation and degradation (REDD) provide a rare opportunity for conservation of tropical forests and biodiversity. Here, we explore the implications of REDD design and implementation options on biodiversity conservation and ways to link REDD with biodiversity conservation. From both a mitigation and biodiversity perspective, the most important immediate steps are to ensure that REDD is included in the new global climate agreement and maximizes the area of tropical forest conserved. It may also be possible to include guidelines or incentives within a REDD framework or in national implementation to channel funding to areas of high biodiversity. However, if the immediate steps above are not taken first, REDD will reach neither its mitigation nor its biodiversity conservation potential.