Thomas Erastus (1524–83) is probably best known for his views on the relationship between Church and State, embodied in the notion of ‘Erastianism’. However, as Charles Gunnoe demonstrates in this impressive biography, this does Erastus a double disservice: not only were his views on Church–State relations more complex than the term generally denotes, but it also overlooks his significant involvement in other spheres. Drawing especially on his published works and extensive correspondence, this volume focuses on the period which Erastus spent in Heidelberg between 1558 and 1580. In the prologue Gunnoe sets the scene, first surveying the history of the Palatinate, and then recounting Erastus’ early career. Part i draws the two strands together, assessing the role that Erastus played – as professor of theology, rector of the university and a member of the church council – in introducing the Reformed religion into the Palatinate. In particular, by highlighting the Zwinglian elements in Erastus’ contributions to the disputes over the lord's supper in Heidelberg, Gunnoe contends that the Reformation of the Palatinate needs to be considered as a ‘pan-Reformed development … and not simply a Calvinist or Melanchthonian achievement’ (p. 52). Connected with this, in the final chapter of the section, Gunnoe argues that Erastus played a greater role in composing the Heidelberg Catechism than has generally been realised. Part ii deals with what Gunnoe presents as the pivotal phase of Erastus’ career, in the late 1560s. This began with a disagreement over the role of discipline. In the face of efforts to introduce a Calvinist-style consistory, Erastus wrote his Explicatio gravissimae quaestionis, a vehement rejection of the practice of excommunication. In so doing he established himself as a leader of the anti-disciplinist party, and placed himself at odds with the Calvinist leadership. The subsequent discovery of an anti-Trinitarian cell within the Palatine Church was used to undermine the anti-disciplinists; Erastus was himself accused of anti-Trinitarianism, but there is no evidence to suggest that this was true. None the less, the fact that he was investigated for heresy indicates the extent to which the current had moved against him. In the wake of these developments, as Gunnoe shows in the third section, Erastus turned his attention away from church affairs and on to other intellectual activities. Here particular attention is given to his scientific views, through an examination of his writings against Paracelsus, and also his contribution to witch-hunting debates through his dispute with Johann Weyer over the appropriate treatment of witches. In the epilogue Gunnoe deals briefly with the final years of Erastus’ career, before considering his longer-term legacy and impact. The volume concludes with two brief appendices, including excerpts from a dozen letters concerning Paracelsus, and also a register of his extant correspondence of around 500 letters. This biography makes a strong case for the importance of Erastus’ contribution to a range of intellectual spheres; more than that, it significantly enhances our understanding of many of the tensions which shaped the Reformation in Heidelberg. For both these reasons, Gunnoe is greatly to be commended.