Volcanic mass flows, especially lahars and pyroclastic density currents (PDCs) are among the most destructive volcanic hazards due to their speed, mobility, and the often-unexpected behavior these flows exhibit as they interact with topography. Mitigation of risk associated with PDCs and other volcanic mass flows depends upon accurate forecasting of magnitude and frequency, potential inundation areas, and possible runout lengths. Measurements of PDCs and other volcanic mass flows, their deposits, and their properties are used in model development and refinement, provide natural examples for benchmarking and comparing model performance, inform laboratory experiments, serve as useful analogs when local data are sparse, and define input parameter distributions for probabilistic flow modeling. These properties are numerous and varied and include information such as triggering mechanism, flow type, frequency, volume, velocity, runout length, and mobility measurements. Statistical forecasting methods, including event trees, rely upon databases to establish base-rates for flow frequency. To aid these goals, FlowDat: Volcanic Mass Flow Database has been developed. FlowDat is a comprehensive global database of mass flows, including dome-collapse and column-collapse PDCs, ash-cloud surges, ignimbrites, directed blasts, volcanic ice-slurry flows or mixed avalanches, lahars, and volcanic, non-volcanic and extra-terrestrial debris avalanches. This initial version of the database, ver. 1.0, focuses on PDCs. Forthcoming versions will include lahars and volcanic debris avalanches.