The Céli Dé monks as we see them in the texts associated with their monasteries had a reputation for extreme asceticism. Following their leader, MáelRúain, who had an especially stern reputation for rigorous observance, they believed heaven had to be earned by saying many prayers, by penitential practices and by intense personal effort and striving on the part of each individual monk. To this end, they engaged in such practices as rigorous fasting, long vigils, confession of sins, strict Sabbath observance and devotional practices involving many prayers. Their view of humanity and of creation generally was negative and they saw God as a stern judge. However, there was another aspect to Céli Dé monasticism which we see in the Félire Óengusso, the metrical martyrology compiled by Óengus the Culdee, a monk of Tallaght. We see from his Félire that he understood holiness as a gift of God’s grace, both for the saints in heaven, whom he describes as ‘radiant’ and ‘shining like the sun’, and for those still on earth, through the mercy and graciousness of God himself. His Félire was compiled as an act of devotion to Jesus and the saints, whom he addresses in terms of great warmth, tenderness and intimacy, in expressions which prefigure the language of the medieval mystics. So by studying the lives of these two monks, MáelRúain and Óengus, his protégée, as case studies, we can see that for the Céli Dé, holiness was less a matter of ‘either asceticism or mysticism’, but rather ‘both and’.