Councils have been of fundamental importance to the historical development of the Catholic Church. From the First Council of Nicaea in 325 CE to the reforming Second Vatican Council of 1962-5, the conciliar movement has more often than not represented the interests and prerogatives of the mass of the frequently - especially from medieval times - as a bulwark against the untrammelled supremacy of the Pope. Norman Tanner is arguably the outstanding scholar of church councils writing in English and his work provides an essential framework to our understanding of the development of Western Catholicism. In this volume, which assembles some of his best work on the topic, he reflects on the legacy of conciliarism, and shows how and why the apostolic spirit of Nicaea was to resurface at Vatican II.