Habitat loss and climate change are two of the most important threats to biodiversity in the tropics. The climate mechanism to Reduce Emissions from Deforestation and forest Degradation (REDD+) can therefore, in theory, address both of these threats by funding forest conservation and slowing climate change. However there are concerns that, if not properly planned, REDD+ could in practice negatively impact biodiversity. In this thesis I introduce the emergence of biodiversity concerns in REDD+ and the relevant safeguards developed at the international negotiations. I present a conceptual framework for understanding opportunities and risks for biodiversity in REDD+, bringing together the literature on biodiversity co-benefits and safeguards. In the last seven years, REDD+ went through a readiness phase and was piloted in over 300 subnational initiatives across the tropics in preparation and anticipation for inclusion in the future global climate regime. I assess 22 of these REDD+ initiatives located in six countries and explore how biodiversity considerations are incorporated into the project design and the challenges faced in delivering biodiversity co-benefits. Many project developers demonstrated strong intentions to safeguard biodiversity, only a handful had explicit goals and interventions targeting biodiversity conservation; often citing the lack of capacity and incentives to protect biodiversity as challenges. I then focus on Indonesia where I use spatially explicit methods to explore the relationship between carbon and biodiversity and the potential for 1st generation REDD+ initiatives to deliver biodiversity benefits. I show that carbon and biodiversity are not correlated in Indonesia; while REDD+ initiatives tend to be (perhaps surprisingly) located in forests important for biodiversity, these are not necessarily the most threatened by future deforestation, thus limiting the contribution of REDD+ to conservation. I then focus on two newly approved subnational REDD+ initiatives and explore how the challenges in implementing REDD+ (especially the slow approval process and reduction in the proposed project area) have impacted orangutan conservation. I show that the Indonesian government will have to re-assess the way in which REDD+ projects are currently being approved if it is serious about its commitments toward orangutan conservation and emission reduction. This study strengthens the notion that REDD+ has the potential to deliver huge benefits for tropical forest biodiversity, especially when located forests most threatened to deforestation. However, progress of REDD+ at the international negotiations have been slow and its inclusion as part of the future climate regime is still uncertain in spite of the urgency of climate change and the potential irreversible negative implications a failed global REDD+ mechanism will have on climate, people and biodiversity.