This report examines the nature of floods, focusing in particular on the important function of flood volume retention and the conveyance of excess water out of river basins. Based on this account, it discusses flood management options that can be implemented as part of a proactive approach, one that seeks to avoid the disasters that may result from a “wait and see” approach. In this context, it describes the role of flood hazard and flood risk mapping in decision making. The note also explores the distinct roles and comparative advantages of structural and nonstructural measures in managing flood risk. In addition, it provides guidance on flood risk assessment methodologies, including the role of numerical simulation models and their data requirements, and also includes a summary of the key principles of flood risk management. All these parts together serve to demonstrate the importance of understanding flood phenomena and assessing flood risks.