Paul Gerhardt (1607–76), one of the most important Lutheran hymn-writers, was part of a significant inter-confessional dispute in Berlin in the seventeenth century. This study seeks to examine and analyse comprehensively the dispute and Gerhardt's role in it, without reducing that dispute merely to an episode in Gerhardt's life. Elector Frederick William i of Brandenburg was Reformed; Lutheran and Reformed clergy and laity had coexisted in Berlin for some decades before the elector sponsored discussions in the hope of reaching some agreement between the confessions. After a chapter providing background, one chapter is devoted to each of three phases of the dispute. The examination of the first phase, developments to 1662, includes biographical information on the most important participants. The chapter on the 1662/63 ‘Kolloquium’ details the discussions between the parties and the failure to reach agreement. The Kolloquium was unable to overcome basic theological differences; Gerhardt played a key role in expressing Lutheran views and encouraging his Lutheran colleagues not to compromise. The chapter on the last phase discusses Frederick William's response to these developments and the consequences of the dispute. In September 1664 Frederick William issued an edict of toleration which mandated not only confessional toleration but also a halt to confessional polemics and criticism directed at the other confession. Gerhardt and other pastors refused to promise to obey the edict; they lost their positions. Ironically, Frederick William's efforts toward theological agreement had precisely the opposite effect: a sharpening of differences in faith and practice and worsening relations between Lutherans and Reformed. A final chapter draws conclusions. Appendices contain a listing of all the statements that Gerhardt made about the dispute as well as the texts of six previously unpublished opinions that Gerhardt wrote about it. The author strives throughout to understand Gerhardt and other participants in terms of their own times rather than in terms of later categories of tolerance. For Ruschke, the Berlin dispute is not only key to understanding Gerhardt but also shows ‘that ecumenical thinking cannot be successful through relativizing confessional teaching or leaving out specifics that divide the confessions’ (p. 528); rather, it can only be successful when these are named. This work presents a thorough and thoughtful tracing of events and is a contribution not only to Gerhardt research but to the study of Lutheran and Reformed theologies and theologians in the seventeenth century and their relationships.