This project was initiated following discussions between BGS and The Crown Estate (TCE) in the light of data from the proposed Round 3 offshore wind farm (OWF) (Celtic Array) being provided to the TCE following the return of the Round 3 licence. TCE make data from marine activities publicly available on the Marine Data Exchange (www.marinedataexchange.co.uk) as a condition of licensing arrangements. It was the intention to extract geological information from the data that may pertain to other potential users of the seabed in the area. Whilst geological conditions at the Celtic Array OWF are not necessarily representative of the entire Irish Sea, the data is invaluable in improving our understanding of wider geological history and the seabed conditions it creates. It is the intention of this report to integrate the Celtic Array OWF data with that collected for the wider renewable industry, BGS legacy data and maps (Appendix 1), and site investigations made available to BGS by the hydrocarbon industry, to provide an introduction to the geology of the seabed and shallow subsurface of the Irish Sea.