Abstract This article identifies new Latin sources and new Latin and vernacular analogues for noteworthy non-legal passages in late Old Frisian law texts. Several items in Thet Autentica Riocht from Codex Unia and the related “Autentica-Sammlung” preserved in Codex Aysma are shown to descend from Insular catechetical triads (including a triad popularized by Alcuin) that were also adapted by the authors of Old English and Old Norse homilies. Other passages in the Autentica collections can be traced to the works of Gregory and Isidore (likely via a florilegium like the Liber scintillarum), to popular twelfth- and thirteenth-century theological texts like the Stella clericorum and Peter Cantor’s Verbum adbreviatum, and to the Disticha Catonis. Meanwhile, a late, variant conclusion to The Seventeen Statutes is shown to utilize an inexpressibility motif derived from the apocryphal Visio Sancti Pauli that is deployed in similar ways in Old English and Old Norse texts. The identification of these sources and analogues has significant implications for the textual criticism of the Old Frisian works and can also help improve our understanding of their relationship to other medieval European vernacular religious traditions.