Under the Kyoto Protocol, the Clean Development Mechanism (CDM) has the dual objectives of facilitating a cost-effective way of meeting greenhouse gas emission reduction targets and contributing to global sustainable development. Due in part to a lack of consensus on definitions of sustainability and sustainable development and a lack of capacity to address these concepts, there is a risk that CDM projects may fail to move the host country towards sustainability. We suggest the use of a scientific, principle-based definition of sustainability to guide project participants in their decision-making process. We propose a user-friendly project planning tool – CDM Select – that can build capacity for project developers to employ a strategic, whole-system approach to sustainable development and increase the likelihood that CDM projects move society towards sustainability. Early review of CDM Select by experts and practitioners in the CDM arena indicate that it has strong potential to assist in these efforts.