This volume offers a critical edition of the Gospel of John according to the Harklean version (615/6 CE). The work is divided into three parts. The first part consists of the introduction, a description of the twenty-two manuscripts, and the preliminaries to the edition, including the explanation of the apparatuses, various Harklean signs, and, more broadly, the editorial policy of the volume. The second part provides the critical edition, which aims to present the extensive and complex data found in the Harklean manuscripts. There are five apparatuses: the witnesses tab, the apparatus to the lemma, the apparatus to the signs, the apparatus to the marginal notes, and the presentation of the explanatory notes. Diverse marginal notes (variant notes, Greek notes, explanatory notes, the Eusabian apparatus, and liturgical notes) are also included. The third part consists of a preliminary commentary on the edition. It addresses the still obscure history of the Harklean version, its particular features, and the process of its transmission in various manuscripts. This part also offers an edition of the marginal explanatory notes and liturgical notes.