John Williamson Nevin and Philip Schaff were the originators of the quite distinctive mid nineteenth-century Mercersburg theology associated with the German Reformed Church seminary at Mercersburg, Pennsylvania. Nevin had been a Presbyterian, and trained in theology at Princeton under the biblical scholar, Charles Hodge. His teacher would later become his fierce critic. Nevin's studies led him both to question and resent the liberal and subjective theology of New England Puritanism, and particularly the emotional and doctrinally light revival methods of Charles Finney. Nevin's historical studies led him back to the Reformation Confessions, and he found himself more at home in the German Reformed Church in America, and became a professor at the Mercersburg seminary. Mercersburg theology has been seen as a Reformed version of British Tractarian theology. In The mystical presence (1846) Nevin surveyed the historic confessions on the Lord's supper, and particularly Calvin's writings, and claimed that Calvin's mystical presence and mystical union was the proper Reformed sacramental theology. Charles Hodge, was outraged by the book, and eventually wrote a hostile review arguing that Nevin had misrepresented Calvin and championing a more Zurich-flavoured theology. It is generally accepted that Nevin's subsequent rebuttal demolished Hodge in logic and learning, and Hodge never attempted a further reply. Nevin and Schaff were later involved in the compilation of a new liturgy for the German Reformed communities – the ‘Provisional Liturgy’ of 1857. This latter, which was not in the end adopted, drew on the liturgy of the Catholic Apostolic Church or ‘Irvingites’ as they were called. It restored a eucharistic prayer after the form of the classical anaphoras, and articulated the teaching of Calvin's 1559 Institutes and the Confessio fidei gallicana, and would have steered the denomination away from the Reformation's bad habit of using exhortation and explication in liturgical rites in place of euchology. The ‘Provisional Liturgy’ was a good hundred years before its time. This edition of The mystical presence is the first volume in a series of reprints of Mercersburg theological works, and Nevin's is a classic. It is a reminder that the Calvin of the last edition of the Institutes and the Confessio fidei gallicana is not the same as the conciliatory Calvin who signed the Zurich Consensus. Calvin's use of ‘exhibit’ and ‘instrument’ for the bread and wine in the two former works do indeed legitimise Nevin's case, though Hodge could have appealed to the Calvin of the Consensus to vindicate the Zurich-type theology that seems to have been the New England default position. The mystical presence does not make easy reading, especially if read out of context, but the introduction by Linden J. DeBie is extremely helpful in this respect. The German Reformed Church in the USA later merged, and eventually became part of the very broad, and not very confessional (thanks to the New England Congregationalists) United Churches of Christ. The mystical presence should be required reading for all UCC theological students, for it is as much their heritage as are the works of Jonathan Edwards.