The postwar period has witnessed a veritable revolution in the attitude of coastal states to their adjacent offshore areas, due principally to a growing appreciation of the resources available in such areas (particularly petroleum, but also fish, metal nodules, gravel, sulphur etc.), but including also a desire to control certain activities in such areas, such as scientific research and the dumping of wastes. Thus there has been a rapid movement from a situation where coastal states conventionally restricted their offshore jurisdiction to a narrow three-mile strip, to one where many states have laid claim to vast expanses of offshore territory. The Irish Republic has, if anything, been in the vanguard of this movement, and the purpose of the present paper is to outline briefly the manner in which the Irish government has gradually extended its area of offshore jurisdiction in the context of evolving international thinking on the subject.