Missionaries are people who operate on the border between their own community and another. The confessional frontier between the Christian and the Jewish communities in Prussia offers a privileged vantage-point from which to analyse the relationship between them. This is the first study to make comprehensive use of the archives and publications of the various Prussian institutions and societies that set out to convert Jews to Christianity. No other body of documentary evidence presents as informed and sustained a commentary on the 'Jewish Question' as it evolved in Prussia during the period covered by this book. Spanning over two centuries of protestant missionary activity, this book examines the ways in which theological, social, and racial themes intertwined in the relationship between the Christian majority in Prussia and the Jewish minority in its midst. These themes are analysed within the context of the rapidly changing relationship between religion and politics in the Prussian state, for 'Jewish Questions', as this book shows, were intimately connected with 'Christian Questions' of equal political and social consequence. This study sheds light on a facet of Jewish-German history that has been overshadowed by the rise of racial antisemitism and the ultimate tragedy of the Holocaust.