Book excerpt: Secure supplies of water, food and energy are essential to human dignity and well-being around the globe. Their vitality is dependent on healthy ecosystems supporting thriving biodiversity. All four elements are inter-related in that actions to govern one will automatically affect the others -- known as the Nexus. Global demand for the first three elements is increasing due to population growth and rising per capital incomes in developing countries, with steadily worsening results for the fourth. The Nexus elements are also subject to increasing pressures from climate disruption in the form of more frequent and severe flooding, droughts, storms, pest outbreaks, and extreme heat. Nature's capacity to moderate these impacts is also being eroded by rapid, widespread land use development and associated pollution. The combination of increasing demand, decreasing supplies, and rapidly changing hydro-climatic conditions at all points of the Nexus requires transformative policy responses that encompass economy, equity, social justice, fairness, and the environment. The Climate Nexus outlines these challenges and offers a pathway to resolving them.