This paper synthesizes principles and concepts about how voluntary carbon market compensation for reduced deforestation - market-based REDD - can help cut global emissions equitably and effectively, while contributing to development goals, protecting biodiversity and watersheds and benefitting indigenous and rural peoples and tropical nations. Several of these principles have also been articulated by various governments as well as Amazonian social movements. This paper also addresses questions that some NGOs and policy makers have raised about how REDD would work.