This thesis is a heuristic and argumentative study of the significance of Neoplatonism in the religious thought of the French Catholic revival of the seventeenth century. Taking the broad corpus of Neoplatonic thought - classical, patristic, mediaeval and, especially, that of the Florentine Renaissance - as its starting-point, it deals briefly with the reception and exploitation of Neoplatonic ideas by the French Humanists, before proceeding to consider the seminal influence of the <u>cercle Acarie</u> in the late sixteenth century. It is in this spiritual group of distinctly mystical bent that we discern the beginnings of a profound movement of religious thought greatly inspired by Neoplatonism, with its ultimate origins in the years predating the Reformation, and which continued to play an important part in seventeenth-century philosophy and theology. This Neoplatonic movement is exemplified by the Order of Capuchins and the Congregation de l'Oratoire, and the main part of the thesis concerns these two religious groups in which the continuity, consistency and, indeed, inescapability of the Neoplatonic tradition are readily apparent. Amongst the Capuchins, the development away from abstract mysticism towards more Humanistic apologetics directly influenced by the Florentines is charted. With regard to the Oratoire, we have attempted to illustrate and demonstrate its pervasive spirit established by its founder and the nature of the Neoplatonism of its members whose fundamental thought and spirituality were informed by Dionysian mysticism and Augustino-Platonic idealism; the problems raised by the thought of Descartes are also considered in our survey of later Oratorians. The final three chapters are devoted to Malebranche, Bossuet and Fenelon, respectively, three major thinkers of the seventeenth century who embody the philosophical, the Humanistic or apologetic and the mystical strains of Neoplatonism that we have identified and which we believe are essential to the Catholic reform of the late sixteenth and seventeenth centuries.