Contents -- Acknowledgments -- Introduction -- Chapter One. The Portion of Book I of the Elements Missing from MS Leiden 399.1 but Present in MS Qom 5365, according to the Edition of Rüdiger Arnzen -- Lo Bello's Notes -- Chapter Two. The Second Treatise of the Book of Euclid on the Elements -- Besthorn's Notes -- Heiberg's Notes -- Lo Bello's Notes -- Appendix I. The al-Hajjaj Edition of Book II Preserved in MS Persan 169 of the Bibliothèque Nationale, Paris -- Appendix II. The al-Hajjaj Edition of Book II Preserved in MS Escorial Ar. 907 -- Chapter Three. The Third Treatise of the Book of Euclid on the Elements -- Besthorn's Notes -- Heiberg's Notes -- Lo Bello's Notes -- Chapter Four. The Fourth Treatise of the Book of Euclid on the Elements -- Besthorn's Notes -- Heiberg's Notes -- Lo Bello's Notes -- Bibliography -- Index.