‘Commissars in cassocks’ was the derisive name the Orthodox faithful gave to those priests who sought to forge a synthesis between Bolshevism and Christianity. Renovationism was the official name for this movement which arose out of the frustration of a section of the Orthodox Church at the failure of all attempts since the 1860s to reform the Church. After the October Revolution the renovationists seized control of the Church with the aid of the Bolshevik state. While the renovationists may have been sincere in their attempts to create a legitimate place for themselves in the new socialist order, the Bolsheviks were utterly cynical in their use of renovationism as a tool for dividing and weakening the Church. The renovationists were rejected by the vast majority of the faithful who recognised immediately the Faustian bargain they had made with the Bolsheviks. Isolated from believers and despised by the new regime, the renovationists gradually dwindled into insignificance until Stalin ended the movement in 1946. The state decided that a compliant but utterly marginalised Orthodox Church suited its purposes better than a failing attempt to synthesise Bolshevism and Christianity. Edward Roslof has produced an authoritative account of this movement. His book is based on extensive work in central and local archives and on an impressive command of the secondary literature. His material has been organised around ‘neo-institutional sociology’, making particular use of two sociological tools: isomorphism and decoupling. All of which seems a rather convoluted way of saying that organisations under pressure take on some characteristics of more successful organisations while rejecting others. In spite of this, the story is clearly and efficiently told. Roslof's work is particularly valuable in that it traces the history of renovationism from its precursors in the 1860s down to its demise in 1946. He is particularly good at showing us how the most enthusiastic supporters of the synthesis between Bolshevism and Christianity adopted many Bolshevik tactics in their attempt to take over the Church: the seizure of power by a minority, the centralisation of power, the purging of opponents and so on. Given that organisational adaptation and accommodation is one of the leitmotifs of the book, it would have been interesting if the author had considered what the Bolsheviks had taken from Orthodoxy, such as an all-embracing worldview, a set of sacred texts, a monopoly of interpretation, paranoia over heresy to name but a few. That aside this is a fine book which gives us a definitive account of the renovationist movement.