This document is the fourth in a series of hazard-specific risk assessment modules, compiled as part of the Words into Action Guidelines on National Disaster Risk Assessment by UNISDR. This section provides a general introduction to the assessment of flood hazard. This section presents some highlights on the most developed practices for flood risk assessment (FRA) without entering into the details of specific methodologies. It will try to clarify the states of research and practice in FRA in relation to different uses of flood hazard and risk information. It will also discuss the issue of scale, the challenge in capturing flood correlation on large-scale events, the need to consider climate change, and the strong links with other perils determining complex multi-hazard scenarios.