This work retraces the history of the Romanian Greek-Catholic Church and its relations with the Holy See in the second half of the nineteenth century. This was a defining period for the completion of the institutional and constitutional organisation of the Greek- Catholic Church in Transylvania. In an era of profound political and ecclesiastical transformations, which affected both the Austrian Empire and Transylvania, the Romanian Greek-Catholic Church underwent an extensive and complex restructuring process even though, as an ecclesiastical province of the Oriental tradition, it preserved its own patrimony of canonical and disciplinary rules in the context of the Catholic Communion. This was a time of highly dynamic and intense relations with the Roman Apostolic See, at the end of which the Greek-Catholic Church from Transylvania entered the twentieth century with a welldefined identitarian physiognomy and a distinct individuality. It was a tortuous process marked by conflict and resolution, expectations and disappointments, turmoil and searches, regulations and enactments, at the end of which the Transylvanian Greek-Catholic Church joined the ranks of the other Eastern Catholic Churches, the Ruthenian and the Maronite Churches, in particular, whose canonicaldisciplinary reorganisation had been completed more than a century before. The book is structured into four parts, which focus on the most significant institutional, ecclesiological and identitarian aspects of the relations between the Roman Apostolic See and the Greek-Catholic Church in Transylvania. The research is based on a vast unpublished documentary material, preserved in the Vatican Archives, the archives of the Romanian Greek-Catholic Church and the imperial archives of Vienna, consistently reinforced by and correlated with the latest findings of ecclesiastical historiography in this field.