Allegations over atrocities committed in Ireland by the English throughout the early modern period have generated bitter debate but little genuine insight. The Cromwellian Wars of the 1650s, however, are widely acknowledged as one of the most traumatic episodes in Irish history. According to English accounts, Ireland suffered a demographic collapse in the face of total war, which included the widespread killing of captured soldiers and Catholic clergy, as well as the deliberate targeting of the indigenous community and the destruction of the country’s infrastructure. These brutal tactics triggered a major famine, which in turn enabled the spread of diseases such as plague and dysentery, killing tens of thousands in the process. Following their military victory, the English transplanted thousands of Catholic landowners, and their dependents, to make way for a new Protestant settler community, and forcibly transported significant numbers of men, women and children across the Atlantic to work in New World colonies. Few today would argue that the excesses of the Cromwellian conquest of Ireland constitute a major war crime but to date nobody has specifically charged the government of the English republic with genocide. This chapter will determine whether in fact there is a case to answer.