When Henry VIII attempted to introduce the Reformation into Ireland in 1537, the dissolution of the monasteries was begun. Somewhat later, relics and images were destroyed and the dissolution was completed. The native chieftains were conciliated by a share of the spoils and received English titles, their lands being re-granted under English tenure. It was Henry's policy thus to conciliate the Irish and to leave them under their own laws. An English commission held courts throughout the island, but Irish right was respected, and the country remained peaceful. 

In the Parliament of 1541, attended for the first time by native chieftains as well as by the lords of the Pale, Henry's title of Lord of Ireland, which had been conferred by the papacy, was changed to King of Ireland. The religious changes under Edward VI and Mary I had little effect on Ireland. 

Although Mary was herself a Roman Catholic, she was the first to begin the colonisation of Ireland by English settlers. The Irish people of King's County and Queen's County (present-day Offaly and Laois, respectively) were driven out and their lands given to English colonists. 

Elizabeth I at first followed her father's policy of conciliating the Irish chieftains, but the rebellion of the Ulster chieftain Shane O'Neill caused her policy to become more severe; an act was passed dividing all Ireland into counties, and the commissioners of justice were invested with military powers, which they used in arbitrary fashion.