The ‘León Antiphoner’, León, Cathedral Library, MS 8, is the most complete manuscript containing Old Hispanic chant, comprising Office and Mass chants for the whole church year. As such, the León Antiphoner is the most studied Old Hispanic manuscript. Despite this, its dating is controversial and hypotheses have ranged from c. 906 (Menéndez Pidal) up to the eleventh century (Zapke and others). In this article, the dating and early history of the manuscript are reconsidered and an entirely new perspective is brought to bear on the questions of when, where, and for whom the manuscript was written. The reinterpretation of the cryptographic inscriptions found at the bottom of fols. 128v and 149r has made it possible to identify the patron of the Antiphoner as San Froilán, Bishop of León, and to date the manuscript’s production to the years 900–5. The scriptorium of the monastery of SS Cosmas and Damian in Abellar is suggested as the likeliest place of production of the Antiphoner.