The preaching of the Christian message, Fr de Broglie points out, has always been accompanied by an appeal, more or less explicit, to 'signs' or 'motives' which draw men to assent to its divine origin. There is no treatise on faith, no manual of apologetics in which these signs do not appear and play their part. This book studies, then the 'signs of credibility', the signs which form the guarantee of Christian message. A study discussing the part which signs play in the act of Faith, and the links which join them and subordinate one to another is needed to fill a gap in theological writing, especially in English at the present time.