This book is, simply put, the best, most well-rounded approach to the theological development of Martin Luther written in at least the last fifty years. Its title alone, the ‘early’ (‘frühe’) Luther, makes clear that Hamm has managed to overcome the old distinction, first coined by German Pietists, between the ‘young’ and ‘old’ Luther. That it also speaks of stages (‘Etappen’), demonstrates that he has wisely abandoned the search for Luther's breakthrough and tower experience (also beloved of Pietism) in exchange for a far more sober, well-grounded examination of the (quite frankly) rich resources from Luther's early theological career and the multifarious shifts that they describe. Hamm thus takes seriously the arguments of both those who favour an early dating of Luther's Reformation ‘breakthrough’ and those who insist that it occurred later. Through this book, Hamm can now lay claim to being the true successor to his teacher, Heiko Oberman, in that he combines a careful examination of individual Luther texts with a vast knowledge of late medieval theology and piety. The early Luther was thoroughly late medieval. Hamm has gone one better than Oberman, however, by showing just how Luther's own early struggles with late medieval understandings of salvation in the monastery led him first to a radical encounter with God's wrath which even the advice of his mentor and confessor, Johann von Staupitz, did not quell. This struggle (‘Anfechtung’, especially described in ch. ii) in turn led to other adjustments in Luther's theology, as he first radically separated human incapacity to save from God's mercy while, at the same time, abandoning late medieval understandings of justification, which centred on love, for a new construal of faith that combined hope and humility with God's unshakeable truth that comes from the outside (especially chs i, iii). In all of this, Hamm argues, Luther shed an approach to salvation dependent upon the qualities in the human soul for a relational theology based solely upon God's descent into human misery on the cross. In a final phase of this development, Luther then discovered the centrality of the external Word of promise that the Holy Spirit used to create and sustain this faith-filled relation to God. On the basis of these crucial introductory chapters, Hamm then turns to specific, crucial texts – the 95 Theses (ch. iv), Luther's tracts on death (ch. v), and The freedom of a Christian (chs vi–vii, the latter chapter already published in an English version in Lutheran Quarterly) – before examining Luther's peculiar mystical theology (ch. viii). A final chapter, which had its origins in a less academic setting, summarises Hamm's insights in an accessible way. If there was ever a book on Luther that deserved to be translated into English, this is it. A few minor adjustments might be made to such an edition. Some of the English sources (especially Steinmetz on von Staupitz and Ozment on late medieval mysticism) could be added. Hamm might also discuss Luther's humanism (à la Helmar Junghans), which contributed greatly to his methodological maturation and, as Rolf Schäfer has shown, even helped Luther (through Erasmus via Philip Melanchthon) to come to a new understanding of gratia (grace) as God's favour and mercy. Incidentally, the phrase ‘the world is too narrow’, which according to Hamm Luther borrowed directly from Johannes Tauler, Luther himself claimed to have learned from Augustine (Table Talk, no. 5945).