This Atlas presents data collected during the IWDG ISCOPE I and II projects, the IWDG/GMIT Marine Mammals and Megafauna in Irish waters project, the IWDG Ferry Surveys Programme and the IWDG casual and effort-based sightings scheme between January 2005 and January 2011. Distribution and relative abundance data are presented on a European Environment Agency 50 km2 reference grid and where sufficient data existed, seasonal distribution and relative abundance maps are presented.