Besides his importance as a Christian mystic, St. Symeon - The New Theologian is a valuable source of information concerning the objectives of a spiritual father and his clients, the kinds of training given by a father to his disciples, and the difficulties encountered in the relationship. These and kindred matters are considered in some detail in this study, which comprises an examination of Symeon’s background, his experience as a disciple and a spiritual father and of the teaching he gave in the latter capacity. The author has been able to make use of three letters written by Symeon the texts of which have not yet been published.