Holy Trinity Greek Orthodox Church (Griechenkirche zur Heiligen Dreifaltigkeit) is a Greek Orthodox Church Cathedral in the first district of Vienna, Austria, in the historic Greek neighborhood of Vienna's Innere Stadt. The neighborhood has also been known as the "Fleischmarkt".
Since 1963 the cathedral has been the seat of the Greek Orthodox Metropolis of Austria (the Ecumenical Patriarchate of Constantinople: the Metropolis of Austria and Exarchate of Hungary and Middle Europe).
Religion in Austria is predominantly Christianity, adhered to by 68.2% of the country's population according to the 2021 national survey conducted by Statistics Austria. Among Christians, 80.9% were Catholics, 7.2% were Orthodox Christians (mostly belonging to the Eastern Orthodox Church), 5.6% were Protestants, while the remaining 6.2% were other Christians, belonging to other denominations of the religion or not affiliated to any denomination. In the same census, 8.3% of the Austrians declared that their religion was Islam, 1.2% declared to believe in other non-Christian religions (including Buddhism, Hindusim, Judaism and others), and 22.4% declared they did not belong to any religion, denomination or religious community.