Evangelical Church of the old-Prussian Union

Prussian Union of churches
The union created one of the largest Protestant bodies in Europe, bringing together a large part of German Protestants into a single church. 1817 Prussia in dark blue.
Classification	Protestant
Orientation	United Protestant (Lutheran & Reformed)
Region	Prussia
Headquarters	Berlin
Origin	1817
Merger of	Lutheran and Reformed congregations in Prussia

The Prussian Union of Churches (known under multiple other names) was a major Protestant church body which emerged in 1817 from a series of decrees by Frederick William III of Prussia that united both Lutheran and Reformed denominations in Prussia. Although not the first of its kind, the Prussian Union was the first to occur in a major German state.

It became the biggest independent religious organisation in the German Empire and later Weimar Germany, with about 18 million parishioners. The church underwent two schisms (one permanent since the 1830s, one temporary 1934–1948), due to changes in governments and their policies. After being the favoured state church of Prussia in the 19th century, it suffered interference and oppression at several times in the 20th century, including the persecution of many parishioners.

In the 1920s the Second Polish Republic and Lithuania, and in the 1950s to 1970s East Germany, the People's Republic of Poland, and the Soviet Union, imposed permanent or temporary organisational divisions, eliminated entire congregations, and expropriated church property, transferring it either to secular uses or to different churches more favoured by these various governments. In the course of the Second World War, Church property was either damaged or destroyed by strategic bombing, and by war's end many parishioners fled from the advancing Soviet forces. After the war, complete ecclesiastical provinces vanished following the flight and expulsion of Germans living east of the Oder-Neiße line.