The Leibniz Institute of European History (IEG) in Mainz, Germany, is an independent, public research institute that carries out and promotes historical research on the foundations of Europe in the early and late Modern period. Though autonomous in nature, the IEG has close connections to the Johannes Gutenberg University Mainz. In 2012, it joined the Leibniz Association.

Joseph (Adam) Lortz was a Roman Catholic church historian. He was a highly regarded Reformation historian and ecumenist. Beginning in the 1940s, Lortz made his ecumenical views available to general readers as well as to scholars in order to promote reconciliation between Catholics and Protestants. His writings played a role in the thinking that manifested itself in the Second Vatican Council's Decree on Ecumenism, Unitatis Redintegratio. What was not widely known, however, was Lortz's involvement with Nazism from 1933 until 1937. His Geschichte der Kirche (1932) portrayed the church of the 1800s and the 1900s as the bastion of divine truth and moral values amid what he considered the decay of Western society.