This study of the imitatio Christi in the life and thought of Charles de Foucauld, soldier, explorer, Trappist, hermit, and missionary-monk (1356-1916), is written against a background of common psychological, ethical, and theological questions about the validity of any attempt at making the imitatio Christi a policy for Christian living. Part One has the dual function of being a survey and assessment of ways of thinking about imitation in human life generally, and about the imitatio Christi in particular, and also providing a context in which De Foucauld'e own interpretation may be assessed. The study of imitation argues that it is an ubiquitous and essential activity, and although complex and not without problems in some of its forms, is capable of contributing to personality development throughout life. The survey of Christian thinking about the Imitatio Christi concludes that the- biblical arid traditional basis for it is strong, and that much current criticism or neglect of the doctrine stems from a general existential standpoint rather than from theological objections. In Part Two the practical consequences of taking the imitatio Christi as a rule of life are traced through the letters and many hitherto unused writings of De Foucauld. The gradual modification and simplification of his concept, based initially on the seventeenth century idea of imitating the 'hidden life' of Jesus at Nazareth, and a monastic interpretation which stressed the rule of 'enclosure', is traced both theologically and biographically. Particular attention is devoted to the influence of St. Teresa of Avila's life and teaching, and to De Foucauld's under-standing of her ascetical and mystical theology, whilst the biographical study illustrates how he gradually came to an integrated self and self-concept, through simplifying his complex preconceptions about the requirements of the imitatio Christi by the application of its basic principle of seeking the will of God through the love of Christ in facing the concrete demands of every day situations. The thesis concludes with suggestions as to the permanent significance of De Foucauld's spiritual pilgrimage for the formulation of a doctrine of the imitatio Christi today.