The most sustained steep increase in marine biodiversity took place during the Ordovician. The variety of biogeographical and palaeoecological settings in the British Isles, the historical type area for the Ordovician, makes this a crucial area for understanding the patterns and processes of biodiversity change. Databases on well-constrained spatial and temporal distributions of organisms will be compiled and analysed to answer a series of pertinent questions on the timing, patterns and controls of biodiversity increase and also its implications for the end-Ordovician extinction event. The understanding of these issues will contribute directly and significantly to the global analysis of Ordovician biodiversity change