The Spiritual Canticle (El Cántico espiritual), the central work of the Spanish poet and mystic St. John of the Cross (1542–1591), has long been a subject of textual debate. We refer here to the attribution to St. John of the Cross of the redaction of the Canticle which for over three centuries has been published as the definitive version. The article describes the history of the first publications of the Canticle and helps to understand the difficulties of authenticating this version, preserved only in the manuscripts of copyists. The author highlights the main formal and substantive differences between so-called primitive version and the definitive version, and provides the main arguments and counter-arguments of the controversy regarding the authenticity of the latter version. Furthermore, the author offers her own resolution to this problem, based on her experience of translating both texts. A number of specific words and expressions, an excess of biblical quotations, repetitions of what previously was attributed as St. John’s comments to the poem, among other issues, lead to the conclusion that the composer of this version cannot be St. John of the Cross. The discussion of this issue and the conclusions drawn are of particular importance for the preparation of the first critical edition of The Spiritual Canticle in Russian, edited by the author of the article.