The debate on natural resource scarcity was recently reignited. New scientific findings suggest that humanity has exceeded the planetary boundaries, threatening its own safe operation. Five attributes characterize the new realism of physical and economic scarcity of key resources: lack of undeveloped resource preserves, challenges of exploiting new resources, emergence of new consumers, volatility of resource prices and broadening of actors in governing resources. Of all the natural resources, water, food and energy are most needed to sustain life on earth. These three resources are tightly interconnected, forming a resource and policy nexus. Their insecurity is an impediment to social stability and economic growth. This report traces the debate, analysis and action on the water, food and energy (WFE) security nexus. Considering the complex interactions of these three resources will require new institutional capacity in both industrialized and developing countries. For the nexus approach to achieve the twin goals of human well-being and green growth, sustainability must move center-stage, with attention given to ecosystem services.