Nikephoros Blemmydes is perhaps mostly known nowadays for his autobiographical work, the ‘partial account’, which has been edited and translated by Joseph Munitiz. In his own day he was well known, renowned as a ‘philosopher’, which in his case can be rendered as ‘learned ascetic’, a monastic founder, a respected theologian, and – in his own eyes, at least, as appears from the ‘partial account’ – a saint. Posterity was less enthusiastic; his sanctity was never celebrated, and what survives of his works is found in a few fugitive manuscripts. Evidence of his theological learning is contained in the ‘partial account’, but is better evidenced in his various, brief, theological works, now edited for the first time and translated into French by Michel Stavrou, professor at the Orthodox Institut Saint-Serge in Paris. Blemmydès was involved in the theological discussions that took place after the Fall of Constantinople, leading up to the Council of Lyon, held in 1274, after his death. These discussions mostly concerned the question of the ‘Filioque’, the addition to the western text of the Nicene Creed that affirmed the double procession of the Spirit from both Father and Son. In his long and learned introduction Stavrou argues that we find in these treatises an attempt, not simply to reject the ‘Filioque’, but to engage with the problem of the eternal relationships within the Trinity, to which the ‘Filioque’ provided an answer, either by drawing on Cyril of Alexandria and Maximos the Confessor, who affirm that the Spirit proceeds from the Father through the Son, which Maximos explicitly regards as what the Latin theologians mean by the ‘Filioque’, or drawing on the idea, found likewise in Cyril and developed by John Damascene, that the Spirit ‘rests in’ the Son. The strongest evidence for such a development is, alas, found in treatises not edited here. What we have here, documents connected mostly with dialogues that took place in 1234 and 1250, are careful defences of the eastern position against the west. The letter to an emperor, argued convincingly by Stavrou to be Theodore ii Laskaris, contains an extended discussion and defence of the expression ‘through the Son’. Elsewhere this is not mentioned; the ‘resting in the Son’ formula occurs once, with little development. Already Blemmydes is criticising the west for reliance on syllogistic argument (or deductive logic), rather than on the authority of Scripture and Tradition, though he, too, avails himself of deductive argument. The texts here are very short, and might seem too slender a basis for very high claims for Blemmydes's theological acuity, but the history of engagement between east and west between the Fall of Constantinople and the Council of Lyon is little understood, and this volume – together with the promised companion volume – sheds light where there has been little hitherto.