The ocean drilling programme has over the course of several decades sampled sea floor sediment around the World. When a major explosive volcanic eruption happens a layer of volcanic ash deposits on the sea floor and this layer may be preserved in the cores. Thus the cores contain a record of the Earth's volcanic activity often extending back many millions of years. Up to now there is no global compilation of the data on volcanic ash layers and this is the primary purpose of this project. This global database of volcanic ash layers will provide a critical resource for researchers interested in global and regional rates of volcanism and for establishing the age of time horizons in ocean drilling cores.