The expression Rule of Faith was used from early on to designate the basic theology of the church—the sum content of "apostolic" teaching—as set down in Scripture, (pre)baptismal confession, and apostolic teaching patterns. Based on early Christological formularies and two- or three-limbed Christian confessions to the One God (cf. 1 Cor 8:6; Matt 28:19; 1 Clem. 46:6; Irenaeus, Epid. 6), this language emerged as a first- and second-century response to questions raised both within and outside of the Christian communities. With particular focus on Irenaeus (especially Haer. I, 10.1), but also on Tertullian and Clement of Alexandria, this article seeks to reflect on the origins of the Rule of Faith (regula fidei). The existence of the Rule is traced back to the apostolic period through close association with baptism and prebaptismal teaching patterns (use of traditional Christ-creed material, the Pauline Heis-Theos profession, and dyadic or triadic structuring of the faith). Particular attention is given to pre-Irenaean use of the term canon, Irenaeus's combination of onemembered, two-membered, and three-membered confessions, and to the close relationship between the Rule of Faith and Scripture in Irenaeus, Tertullian, and Clement. Together, these features of the regula fidei constitute a textual matrix within which proto-orthodox Christian hermeneutics by and large operated. Some structural similarities between the scribal nomina sacra practice and the Rule-of-Faith-pattern are noticed.