Most existing accounts of the Catholic Apostolic Church contain serious errors and distortions, often due either to brevity or selectivity. This work is designed to provide an extensive account of this unique body based upon authoritative primary sources. It fills a gap in current scholarship: most other recent works deal with individual aspects of the body, and hence cannot adequately indicate either its overall nature or the way in which its various features are interrelated and underpinned. It has been deemed essential that primary source extracts be a significant feature, because these are extremely difficult of access for scholars (and becoming increasingly so), and because it is necessary to show the precise terms in which Catholic Apostolic theology and practice were expressed. The "history" has been covered by others: it is included here for completeness and in order that a number of errors of fact and certain misunderstandings can be corrected. The chapter on "ecclesiology" deals, for the first time in depth, with the Catholic Apostolic understanding of the nature of man and the ministries deemed necessary for his spiritual welfare, and distinguishes between the different types of prophetic witness. The chapter on "liturgy" considerably extends existing scholarship by providing fresh insights into the typological background of Catholic Apostolic worship on a wider basis than the Eucharist alone. The chapter on "eschatology" provides a new analysis of the sources of Catholic Apostolic eschatology (for the first time including an examination of the work of Lacunza) and of the eschatological understanding of the rites. Finally, the underlying common themes are brought together to expose the strengths and weaknesses of the body; the question of its debt to Eastern Orthodoxy is examined, and its current significance is considered. A classified bibliography is critical for further research, and has therefore been provided.