1. Family papers
The papers contain material relating to the Actons of Naples: Commodore John Acton, his nephew J.F.E. Acton and H. Acton, a midshipman; material concerning the Dalberg family, particularly the family property on the Rhine, at Herrnsheim; a few manuscripts relating to Lord Granville; and the 1st Lord Acton's personal papers, including those covering his early years, his parliamentary career and interest in Ireland, relations with his family, and the period of his life spent in Cambridge.
2. Library development
The collection includes a number of important manuscript series that were acquired by Acton for his library. These include the notes and lecture material of Ernst von Lasaulx, Acton's teacher in Munich in the early 1850s; manuscript and printed material for Acton's project 'The history of the papacy', collected during five years of travel on the continent; documents relating to the history of religion in modern times, particularly French religious history; and manuscripts concerning the history of England, particularly of Roman Catholicism. There are also catalogues of the library made by Acton and by librarians he employed to complete the work.
3. Transcript collection
Acton and his copyists made a series of transcripts between 1865 and 1875 from archives held throughout Europe for 'The history of the papacy'. There are transcripts from archives in Vienna, Venice, Modena, Rome, Naples, Florence, Simancas, Paris, the British Museum, the Public Record Office, the Bodleian Library and other repositories.
4. Business archive
The collection contains a large series of letters of the Paganelli and Cantucii families, merchants in Florence and Spain, dating predominantly from the late seventeenth and early eighteenth centuries. It is not known how Acton came to acquire these papers.
5. Study projects and finished works
Acton's research projects are represented in the collection by his card system and notebooks. The material covers 'The history of the papacy' project, including the Massacre of St Batholomew, the Inquisition, the Council of Trent, Henry VIII and James II; Acton's 'History of freedom'; his work with J.W. Cross on the latter's composition of The life of George Eliot; Acton's writing on Liberal Catholicism, including Church history and biographical material on his close friends Ignaz von Döllinger and Cardinal Newman; and Acton's time in Cambridge, including lectures on the French Revolution and modern history, and material concerning the Cambridge modern history. There are also notes and quotations on a variety of other subjects.