Biodiversity is complex. REDD+ is complex. Monitoring biodiversity as part of REDD+ could therefore add a complexity and cost to REDD+ that stymies rather than promotes progress. A large range of approaches is available to both project- and national-level REDD+ stakeholders in designing purposeful, efective and realistic monitoring systems. To bring clarity to the options, this sourcebook adopts a simple four-stage monitoring framework: Defining objectives: Why monitor biodiversity for REDD+? Selecting indicators: What to monitor for REDD+? Implementation of monitoring: How to monitor for REDD+? Informing relevant audiences: Sharing and using the information generated. Across this framework, the key considerations for REDD+ can be summarised under three criteria for meaningful monitoring: Purposeful: having clearly stated goals and objectives; Efective: being able to attribute changes in biodiversity to its causes; Realistic: being able to achieve this given real-world resource constraints.