Increasing emphasis on social and environmental safeguards for REDD+ in the UNFCCC and work under the Convention on Biological Diversity (CBD) have prompted growing interest in biodiversity monitoring for REDD+, but most discussions of REDD+ monitoring have so far centred on greenhouse gas emissions and removals at national level. Challenges in monitoring biodiversity for REDD+ include choosing which aspects of biodiversity to monitor, the difficulty of attributing particular changes to REDD+ and the likely scarcity of resources for biodiversity monitoring. Three responses can help address these challenges. First, already-agreed policy targets can help to identify what should be monitored. Second, making links to existing biodiversity monitoring and to monitoring to estimate GHG emissions and removals (both remote sensing and ground based inventories) can provide some solutions. Finally, developing clear theories of change can assist in determining which changes in biodiversity can be attributed to REDD+.