Flooding is one of the most common natural disasters worldwide and has the largest economic impact on society. The developing world is particularly vulnerable, as the people there are disproportionately affected by flooding. In Vietnam, flooding occurs annually, and the Thach Han Basin is among the areas vulnerable to flooding. The book describes the process to assess flood risk in the basin. The MIKE model family, including a hydrological model (NAM), hydraulic dynamic model (MIKE 11) and MIKE 11 GIS, was the primary tool applied to create flood risk maps. Risk is herein understood as a function of the hazard and the vulnerability of society to damage due to the hazard. The hazard maps were constructed from the duration maps and the inundation maps. Through field survey and data analysis, land use and population density were chosen as the basis to develop the flood vulnerability maps. Flood risk maps were constructed by integrating the hazard and vulnerability maps.