The present work intends to show that Maurice Blondel's philosophy follows a triadic structure made up by the undissociable bond between thought, being and action, which is not just the resuit of the evolution achieved in the Trilogy but that was already present since L'Action (1893). Firstly we briefly outline the itinerary from L'Action (1893) to the Trilogy, underlining the continuity that Blondel ascribes to his progress coming later to make evident the unity of his philosophical project. Secondly we will consider the aspects revealing a triadic structure in the philosophy of action: the sense of action as mediation, the dialectics of action and the logic of action. Finally we will show how blondelian philosophy, in its characteristic structure, corresponds, quoting the author, to an "unitarian trinity".