András Forgó submitted this work as a dissertation at the University of Mainz in 2005, then modified it only slightly for this edition. The negotiations referred to in the title identify the climax of this short book, following sections providing an overview of church politics in Hungary from 1526 to 1687, Orthodox-Catholic union attempts in Hungary in the late seventeenth century, and Protestant-Catholic relations in the Holy Roman Empire during the same period. The first three sections are based mostly on secondary works and source publications and prepare the reader for the examination of the Protestant-Catholic negotiations in late-seventeenth-century Hungary. In the fourth part, the author provides substantial original analysis of new sources. He draws his findings together in a brief conclusion, then supplies the text of eighteen documents in Latin, most of them published here for the first time.

The discussion of Protestant-Catholic relations in Germany centers on Johann Philipp von Schönborn, the elector-archbishop of Mainz (1647–1673), and his so-called Konvertitenkreis of prominent Protestants whose conversion gained them office in the Electorate. Rojas y Spinola was born in the Netherlands, participated in an irenicist circle during his seminary years in Cologne, and pursued a diplomatic and ecclesiastical career in Germany, Spain, and then Austria where he served as bishop of Wiener Neustadt 1687–1695. After the death of the elector, Rojas organized a meeting with Protestant theologians in Hannover in 1683, though empowered by neither the pope nor the emperor to negotiate a church union. In the end, all but one of the Protestant princes rejected his proposed starting point for union discussions.

For Hungary, however, Rojas y Spinola did receive the requisite powers (Vollmacht) from the emperor to initiate union talks with Protestants in 1691. He convened meetings with German Protestants of western Hungary's royal free cities and had some success, but his overtures were rejected by some Catholic bishops, including the primate, as well as by Hungarian Calvinists. The climactic effort of his career, and the chapter to which this book builds, hence ended in disappointment. It is unclear what documents were discussed at these meetings, but a key 1692 text resembles others used by Rojas in Hannover and in 1660 by the Mainz Konvertitenkreis.

The author concludes that Catholic-Protestant union was more difficult than Catholic-Orthodox to achieve because the theological differences were greater, because the Holy See was unwilling to grant Rojas the power to make the concessions he proposed, and because he could not offer the real social advantages of union that were tendered to the Orthodox. Forgó notes that many key documents on Rojas's mission are missing. It is nonetheless clear that Rojas brought to his projects not only an engaging enthusiasm, but also a genius for self-promotion. The author carefully withholds judgment as to whether Rojas represented real forces and possibilities or was even a fraud. This is a meticulous but inconclusive study of a curious and puzzling chapter in German and Hungarian church history.