With the HOWAS 21 flood damage database, scientists at the GFZ German Research Centre for Geosciences have created a sound data basis for researching flood damage. This data is used to better understand how flood damage occurs and to assess the effectiveness of preventive measures. The estimation of economic damage is an important component in decisions on flood protection measures on the basis of cost-benefit analyses. Compared to other areas of hydrology and water management, however, there is little data available on flood damage in Germany. For this reason, scientists at the Helmholtz Centre GFZ in Potsdam set up the HOWAS 21 database as part of the BMBF-funded program “Risk Management of Extreme Flood Events” (RIMAX) on the basis of scientific findings. In addition to the monetary damage incurred, e.g. to buildings, household goods or business equipment and to land, HOWAS 21 also records data on the impact of the event on the property, the damaged property itself and damage mitigation. Each case of damage is also assigned to a superordinate flood event and a survey campaign (metadata). The attributes in HOWAS 21 are based on catalogs that were defined for each sector through a multi-stage expert survey.