St. John the Baptist Byzantine Catholic Cathedral in Pittsburgh, United States
Classification	Eastern Catholic
Theology	Catholic theology
Polity	Episcopal
Structure	Metropolitanate
Pope	Francis
Primate	Metropolitan William C. Skurla
Associations	Congregation for the Oriental Churches
Region	United States, Czech Republic and Ukraine
Liturgy	Byzantine Rite
Headquarters	Cathedral of Saint John the Baptist, Pittsburgh, Pennsylvania, United States
Origin	1646
Merger of	Union of Uzhhorod
Congregations	664
Members	419,500
Ministers	549
Other name(s)	Byzantine Catholic Church (US only)

The Ruthenian Greek Catholic Church (Rusyn: Русиньска ґрекокатолицька церьков; Latin: Ecclesia Graeco-Catholica Ruthenica), also known in the United States as the Ruthenian Byzantine Catholic Church, is an Eastern Catholic church that uses the Byzantine Rite for its liturgies, laws, and cultural identity. It is one of the 23 Eastern Catholic churches that are in full communion with the Holy See. There are two main communities within the church: American and European. In the United States, the Byzantine Catholic Metropolitan Church of Pittsburgh is self-governing (sui iuris). In Europe, Ruthenian Catholics are immediately subject to the Holy See. The European branch has an eparchy in Ukraine (the Eparchy of Mukacheve) and another in the Czech Republic (the Ruthenian Apostolic Exarchate of Czech Republic).

The Ruthenian Catholic Church is rooted among the Rusyn people who lived in Carpathian Ruthenia. This part of the Carpathian Mountains straddles the borders of the present-day states of Hungary, Poland, Slovakia, Romania and Ukraine. Today, the church is multi-ethnic. Members of the metropolitan province of Pittsburgh are predominantly English-speaking. Most are descendants of Rusyns – including sub-groups like the Boikos, Hutsuls and Lemkos – but the descendants of other nationalities are also present such as Slovaks, Hungarians and Serbs as well as those of non-Slavic and non-Eastern European ancestry. The modern Eparchy of Mukacheve in Ukraine is mostly Ukrainian speaking and remains officially part of the greater Ruthenian Church.