This is an edited collection of Owen Chadwick's principal writings on Lord Acton, the distinguished Victorian historian and founder of The Cambridge Modern History. Some of the pieces are no longer readily available, while one has never before appeared in English. All have been revised, sometimes extensively. Acton (1834–1902) was born in Naples, the grandson of the Neapolitan prime minister Sir John Acton. Educated at Munich University, he sat as a Liberal MP 1859–64, was created a baron in 1869, and in 1895 was appointed Regius Professor of Modern History at Cambridge. This book explains the important aspects of Acton's complex mind and his great contribution to historical studies. Professor Chadwick, himself a former holder of Acton's Regius Chair, is the leading senior authority both on Acton and on matters of church and state in the nineteenth century.