Climate change adds uncertainty to already complex global water challenges. Because climate change affects poorer countries and vulnerable populations the most, the World Bank strives to mainstream climate change considerations into its operations to inform investment and water resources management decisions. Although no standard method has been adopted yet by the Bank, common practice used downscaled projected precipitation and temperature from Global Climate Models (GCMs), as input to hydrologic models. While this has been useful in some applications, they often give too wide a dispersion of readings to provide useful guidance for site-specific water resources management and infrastructure planning and design. Rather than design for an uncertain situation selected a priori, the so-called “bottom-up” approaches explore the sensitivity of a chosen project to the effects of uncertainties caused by climate change. This book summarizes alternatives explored by a group of organizations (such as the U.S. Corps of Engineers, Conservation International, the University of Massachusetts and the Bank) all belonging to the Alliance for Global Water Adaptation (AGWA), to provide practitioners with the tools to adapt to the realities of climate change by following a decision-making process that incorporates bottom-up thinking.