In 1559/60 the parliaments of England, Ireland and Scotland proscribed the practice of Catholicism in their respective kingdoms and prescribed Reformed religious settlements in its place. By the end of the sixteenth century the English and the Scots had become nations of Protestants, but contemporary estimates of the number of Irish Protestants ranged between 40 and 120 individuals. Protestantism in Ireland was born of conquest and colonisation in the seventeenth century. Yet the remarkable contrast in the outcomes of the Reformation across the Atlantic archipelago was not predestined. England and Ireland shared the same Tudor monarchs and the Pale around Dublin was, in effect, an appendage of England. Nonetheless, while Elizabeth I’s religious settlement was a ‘runaway success’ in England it failed to win any significant support in Ireland. Indeed, because Irish women were particularly loath to embrace the new religion no self-sustaining community of Irish Protestants was spawned in the sixteenth century. On the other hand, the Scots created a Reformed Church establishment despite the wishes of their monarch, Mary Stuart, queen of Scots. This chapter adopts a comparative approach to help explain the experiences of Reformation in England, Ireland and Scotland before 1603.