Historians of early medieval monasticism may be forgiven for overlooking Geoffrey Koziol's magnum opus, for the title of his study provides no indication of the important role that cloistered communities play in his argument. This is primarily a book about royal diplomas and the way in which Carolingian rulers between the death of Louis the Pious (840) and the coronation of Hugh Capet (987) used them to make authoritative claims about their right to rule (part i, ‘Instruments of power’). Concomitant with this argument is Koziol's contention that ‘diplomas give us a record of [the] struggles, memories and aspirations’ of late Carolingian kings (p. 4) and are thus expressive of the royal ideologies of individual rulers (part ii, ‘In the footsteps of kings’). But this is also a book that offers important insights about monastic reform in the ninth and tenth centuries. Control of important monasteries was a key factor in the endemic struggles for power that characterise the political landscape of the West Frankish realm in the late Carolingian period. In chapter vi (‘Allying the saints: diplomas and monastic reform’) Koziol makes the case for the role of monastic institutions in the survival of the fragmenting kingdom. He roots the impetus for the foundation of reformed monasteries in criticism of the abuse of church property by Charles the Bald and his allies. Free from secular and episcopal interference, the monks of new foundations like Cluny could pray for the survival of the realm uninterrupted by the distractions of the world. Moreover, monastic reformers like Abbot Odo of Cluny were themselves aristocrats, who had been born into a culture that understood the value of alliance-building and worked to foster amicitia (which Koziol defines as ‘the willing alliance of independent political actors’: p. 312) between secular rulers to mend the political divisions that were rending their society asunder. In doing so, Koziol argues, the reforming monks of Cluny and others like them were instrumental in the survival of the West Frankish kingdom, for in a time of acute political contention they worked in the belief that alliances ‘could reconstitute a kingdom as a moral community – a community of the faithful, a community of the faithful to the king’ (p. 312). This is one of many thought-provoking arguments in a book that is deeply learned and imaginative in its treatment of these sources yet at times rambling, poorly organised and difficult to follow, at once exhaustive and exhausting.