The “branch theory” is an ecclesiological concept of the 19th-century Oxford Movement which holds that the Roman Catholic, the Orthodox and the Church of England are three branches or portions of the One, Holy, Catholic, and Apostolic Church. This teaching attempted to explain the meaning of the unity ofthe Church by stressing that this unity still exists ontologically in spiteof the fact thatthe branches are out of sacramentalcommunion with each other. Each community remains to be a branch of the One Church of Christ provided that it continues to hold some fundamental elements of the Tradition (such as the valid Apostolic Succession of its bishops) which secure the unity with the ancient Apostolic Church. The branch theory basically ground itself on a specific understanding of the notion of schism and on a relativistic explanation of the consequences of the schism for the life of the Church. An understanding of the notion of the schism as an natural and normal phenomenon therefore is a prominent feature of this theory. This study aims to consider some fundamental theological premises which formed a specific context for the origin of the branch theory. This was executed through an analysis of the argumentation of the theology of the Theory which rely on an interpretation of some anthropological, ecclesiological, biblical and patristic notions in order to support its conclusions about the meaning of schism. Influences of some presuppositions inherited from the classical Anglican theology (theory of the ”national Church” and “ecclesiological relativism”) were also examined, as well as influences of some presuppositions inherited from the classical Protestant theology (the notion of the “Word of God” and the theory of the “visible” and “invisible Church”). In final analysis some key factors which probably constitute the main weak points of this ecclesiological teaching were identified as a lack of an eschatological perspective on Church’s historical existence and as neglect of the significance of the Eucharistic communion for the realization of the unity of the Church.