This study of various aspects of Seneca’s religion and theology, drawn from the entirety of his body of work, offers a perspective on the evolution and the adaptation of the Stoic doctrin in the Roman context. The religious phenomenon is considered here simultaneously from two standpoints: the Citizen’s civil religion, as well as the inner piety of the individual. The diversity of a half-philosophical, half-poetical work would warrant a synchronic rather than diachronic view (even taking into account the evolution of the author’s thought), which favors an exegesis based on literary genres and their codes. The first part analyzes the dominant principles of Roman religious consciousness (the opposition religio/superstitio), in the light of critical heritage. The second part demonstrates that Seneca constantly tries to find some value in traditional religious discourse, as well as in the words of the poets. His situation as a philosopher/statesman forces him to make concessions, especially on the imperial cult. The third part constitutes a doctrinal summary of stoic monism and its appropriation by Seneca, who leaves room for a true religious emotion towards the rational deus. The progressive hierophany by an individual growing in wisdom implies a transition from physics towards ethics. The fourth part treats the question of the search for adequate language to define the divinity. The fifth part explores the relationship between the individual and the divinity. Man, heroic in his rise above contingencies, elevates himself through an exercise of thought to the rank of deus, up to communing with the god in pure wisdom, chiefly through philosophical prayer.