The history of the Greek Catholic Churches evolving in Hungary in the 17th and 18th centuries may be best described in terms of a division according to four regions. The first region is the historic Eparchy of Mukacheve (Munkács) comprising thirteen counties in the northeast of the Kingdom of Hungary. Its Greek Catholic Church was created by the Union of Uzhhorod (Ungvár) concluded in 1646. A few decades later, the Greek Catholic Church began to flourish in two other nearby regions. The last decade of the 17th century saw the unification of the Eastern-rite faithful of the Roman Catholic Diocese of Oradea (Nagyvárad) with the Roman Catholic Church, followed by their brethren from Transylvania. The three regions were in close contact: In the course of the establishment and development of ecclesiastical organisation, the borders of the eparchies concerned would change several times. In terms of the ethnic groups living in these regions, the Greek Catholic Churches counted Ruthenians, Romanians, Slovaks and Hungarians among their members. Chronologically speaking, it was in the fourth region where the unionist movement took off first (in the early 17th century), but it would fail to become prevalent among the South Slavic peoples. For better transparency, the written historical sources published on the webpage are arranged under the following headings: