A variety of ensialic Mesozoic and Cenozoic sedimentary basins surround Ireland. Three main periods of basin development occurred. The first, in the Permo-Triassic, produced a series of small rift basins which nucleated along reactivated, generally Caledonian, structures. The second, in the Mid- and Late Jurassic, represents a period of crustal extension and rifting. The third phase reflects thermal subsidence of Cretaceous and Tertiary age, and coincides with seafloor spreading in the North Atlantic. The basins developed in response to general east-west extension. Simple extensional structures, accompanied by crustal thinning, dominated in the north-south-trending Porcupine Basin. The NE-SW-oriented basins in the Celtic Sea, Slyne-Erris-Donegal and Rockall areas developed in a transtensional setting until Early Cretaceous times. The Goban Spur basins, at the confluence of regional structural trends, and adjacent to the continent-ocean boundary, are dominated by transtensional structures. The effects of Early Tertiary Alpine compression are seen especially in the Celtic Sea basins. The basins, whilst having some broad geological similarities which reflect eustatic sea-level variations, differ in their detailed evolution. Each basin experienced unique facets of local structural control, tectonic history and facies distribution.