Every book has a two-fold history; a history before, and a history after its publication. The first can be described only by the author himself; and respecting this. The public im poses Ou him the duty to make no mystery, and, accordingly, to relate to it partly the outward occasions that induced him to undertake the composition of his work and partly to assign the more intrinsic reasons, by which he was determined to the undertaking. Hereupon I have now to communicate to the indulgent reader the following remarks. The present work has arisen out Of a course of lectures, that for several years I have delivered on the doctrinal differences between Catholics and Protestants. On this subject it has been the custom for years, in all the Lutheran and Calvinistic universities of Germany, to deliver lectures to the students Of theology; and highly approving of this custom, I resolved to transplant it to the Catholic soil, for the following reasons. Certainly those, who are called to take the lead in theological learning, may be justly expected to acquire a solid and com prehensive knowledge of the tenets of the religious communities, that for SO long a time have stood Opposed to each other in mutual rivalry, and still endeavour to maintain this their posi tion. Justly are they required not to rest satisfied by any means with mere general, uncertain, Obscure, vague, and unconnected notions upon the great vital question, which has not only, for three hundred years. Continually agitated the religious life of Europe, but has in part so deeply and mightily convulsed it.