This Analytical Brief aims to provide a starting point for discussion on the range of issues that collectively fall under the umbrella of water security, identifying the challenges that lay ahead, the necessity of relating water security to policy development, and offering possible options for responding to these challenges. It underlines the important role that cooperation will play in addressing water security challenges, including collaboration between different stakeholders and across all levels, from local to international. Section 1 introduces the brief and the concept of water security. Section 2 outlines the broad concepts for understanding water issues within the context of security. It establishes the link between water and human security issues, and highlights how water insecurity can lead to fragile and vulnerable societies. It points to the importance of the role of water in transboundary contexts, whether for cooperation, or in tensions or instability, and serves to stimulate the research and policy communities to address water security challenges. Section 3 explores the relevance of water security to policy formulation on a number of key dimensions - from human rights, to development, to the protection of ecosystems. Section 4 highlights the key supporting elements needed to achieve water security - policies, capacities, governance mechanisms and structures - and options for addressing water security challenges.