The nineteenth century produced a number of statesman and church leaders of imposing intellectual stature and historical vision. Among these, two stand out: Manning, who became the most sophisticated champion of modern Roman Catholicism in England, and Gladstone, who defined liberalism both for his generation and for posterity. The two, who first met when they were both undergraduates at Oxford, conducted an intense correspondence which ran for over half a century. Their letters covered important intellectual, political, philosophical and religious questions as well as more personal matters, including identity and self-perception: ‘We are both men who seldom act without a reason’, wrote Manning to Gladstone on 16 March 1861, in response to a note from the statesman saying that it had been ‘an impulse of nature’ which prompted him to ask for a meeting. Besides the apparent triviality of this formal exchange, these comments contained deep insights into the two men's personalities. It is not an isolated example. On the contrary, the significance of this correspondence is considerable. It helps us to understand better the British government's attitude to foreign and imperial matters, including the response to the international crises which accompanied the process of Italy's unification, and the handling of Ireland during the rise of nationalism. More generally, this collection of letters highlights the wider relevance of religious and ecclesiastical issues in the ‘high politics’ of the then world's only superpower. Moreover, it sheds new light on the development of two great minds, whose friendship and disagreements are documented in minute detail. In fact, as Erb notes in his masterly introductory essay (vol. i):

The letters are arranged in twelve sections, with titles such as ‘Confronting the Romeward trend’ (June 1843–October 1844), and ‘Archbishop and Prime Minister’ (December 1868–February 1875), and each volume has a full listing of the letters, which makes consultation both easier and more effective. The last volume contains, as an appendix, the pamphlets which the two great Victorians exchanged as they debated the political implications of the 1870 Vatican Decrees, and particularly the papal claim to infallibility. The international academic community is greatly in debt to Peter Erb for this work, a great scholarly achievement of awe-inspiring breadth and depth, a masterpiece comparable to the Gladstone diaries, also published by Oxford University Press, and edited by the late H. C. G. Matthew.