This essay reassesses the importance of Conor Cruise O'Brien's Parnell and His Party, 1880–90, originally published in 1957, with particular reference to its significance in the history of the British parliament. While establishing the book's continuing relevance, both as a study of a specific political phenomenon and as a model for analysing political movements, the essay questions aspects which do not hold up in the light of subsequent research. In particular, O'Brien's account and interpretation of Parnell's behaviour in 1890–1 in the aftermath of the O'Shea divorce case is shown to be inadequate in the light of more recent research and writing.