The idea of an ‘Irish empire’ has had enduring appeal. It was a rare source of pride promoted by politicians and churchmen during depressed periods in independent Ireland, particularly the 1950s, and the phrase provided an evocative title for at least one popular – and notably sanguine – version of the Irish diaspora's story as late as the turn of this century. In such contexts ‘Irish empire’ can appear simply a wry play on a far more commonly used and, if recent scholarship is to be taken into account, by no means unrelated term, ‘British empire’. Yet as many historians of the Irish abroad, the Irish Catholic Church, and Irish culture more generally have noted, the existence of a peculiarly Irish ‘spiritual empire’ was widely spoken of even as the island's ports were daily choked with emigrants. Nevertheless, the pervasiveness and persistence of the concept, invariably involving the perception of a special, God-given emigrants' ‘mission’ to spread the Catholic religion in whatever part of the world they settled, warrant a more searching analysis than historians in the above-mentioned categories have hitherto devoted to it.