The document summarizes the objectives and structure of CIFOR's Global Comparative Study on REDD+ (GCS-REDD+). The study aims to support REDD+ policy and practice with science-based analysis and tools to help ensure REDD+ outcomes are effective, efficient, equitable, and provide co-benefits. It works in 12 countries conducting policy analysis and 6 countries with 23 REDD+ project sites analyzing impacts on 190 villages and 4,524 households. Key challenges discussed include addressing tenure issues, balancing local livelihoods and forest protection, meaningful community participation, and building technical capacity for monitoring and reference levels. International discussions are found to affect local implementation, and a "no regrets" agenda is proposed