The United Nations World Water Assessment Programme (WWAP) is hosted and led by UNESCO. WWAP brings together the work of 31 UN-Water Members as well as 37 Partners to publish the United Nations World Water Development Report (WWDR) series. Under the theme Water for Sustainable Development, the WWDR 2015 has been prepared as a contribution from UN-Water to the discussions surrounding the post-2015 framework for global sustainable development. Highlighting water's unique and often complex role in achieving various sustainable development objectives, the WWDR 2015 is addressed to policy- and decision-makers inside and outside the water community, as well as to anyone with an interest in freshwater and its many life-giving benefits. The report sets an aspirational yet achievable vision for the future of water towards 2050 by describing how water supports healthy and prosperous human communities, maintains well functioning ecosystems and ecological services, and provides a cornerstone for short and long-term economic development. It provides an overview of the challenges, issues and trends in terms of water resources, their use and water-related services like water supply and sanitation. The report also offers, in a rigorous yet accessible manner, guidance about how to address these challenges and to seize the opportunities that sound water management provides in order to achieve and maintain economic, social and environmental sustainability.