Most agree that the Nine Years War (1594-1603) was a least partly religious in motivation. Curiously enough, while we do know something of the religious issues which protagonists claimed as inspiration, we know little of their own religious practice or convictions. This is especially the case of Hugh O'Neill, earl of Tyrone. Religious conviction is, of course, a notoriously dangerous field of historical enquiry but given that O'Neill propaganda presented him as a Catholic crusader and taking into account the doubts some of his contemporaries raised regarding the sincerity of his religious convictions, it might not be amiss to enquire, in so far as the sources permit, what O'Neill's Catholicism was like.