In the context of a complex ecclesiological analysis, the volume introduces the reader to the study of the doctrinal developments concerning the Trinitarian mystery. In particular the author underlines the historical-speculative contribution of the believing and praying communities. The study?s main focus is in fact the Profession of Faith in God the Father, Son and Holy Spirit of the Church liturgy and personal prayer experience. A great deal of space is devoted to Trinitarian hints embedded in the Old and New Testament. The Author retraces the evolution of Christian theological thought examining its key figures and events since the Apostolic Age. The volume, which is sensitive to educational needs of a sound historical and doctrinal grounding, is absorbing as it highlights contextual factors at the origin of doctrinal statements whose Trinitarian foundations are always carefully highlighted.