Philip Schaff (January 1, 1819 – October 20, 1893) was a Swiss-born, German-educated Protestant theologian and ecclesiastical historian,[1] who spent most of his adult life living and teaching in the United States.

During his time there, he spoke positively of some medieval Catholics and of the Oxford Movement and he was accused of heresy; a church council exonerated him.

His inaugural address on The Principle of Protestantism, delivered in German at Reading, Pennsylvania, in 1844, and published in German with an English translation by John Williamson Nevin was a pioneer work in English in the field of symbolics (that is, the authoritative ecclesiastical formulations of religious doctrines in creeds or confessions).

In 1854, Schaff visited Europe, representing the American German churches at the ecclesiastical diet at Frankfurt am Main and at the Swiss pastoral conference at Basel.

In consequence of the ravages of the American Civil War the theological seminary at Mercersburg was closed for a while and so in 1863 Schaff became secretary of the Sabbath Committee (which opposed the "continental Sunday")[6] in New York City, and held the position till 1870.

Schaff was also, in 1871, one of the Alliance delegates to the emperor of Russia to plead for the religious liberty of his subjects in the Baltic provinces.

He translated Johann Jakob Herzog's Real-Encyklopädie für protestantische Theologie und Kirche (Encyclopedia in Real Terms of Protestant Theology and Church) into English.

Working with the Evangelical Alliance and the Chicago (1893) World's Parliament of Religions, and in Germany, through the monthly Kirchenfreund, Schaff strove earnestly to promote Christian unity and union.