My purpose In this thesis is to study the English Books of Common Prayer of 1549, 1552, and 1559 in their historical setting, in an effort to see the reasons for their creation, to determine the extent of their Catholic validity and to probe the question of their legality. Such an inquiry is historically significant in view of the very large part played in English history by the Church and her standards. It is almost a truism, but one worth repeating, that in order to understand English history it is essential to understand also the formation of England's ecclesiastical establishment.