This work presents to the scholarly world the hitherto unpublished trove of over 500 catchwords that were attached to Masoretic doublet notes in the Leningrad Codex. All the doublets with their catchwords are listed both in the chronological order of their first appearance in the Bible and again on their second appearance. In the Introduction the nature of the catchwords, their purpose, and their relation to other Masoretic notes are described in detail. Because these doublets have up till now remained hidden and virtually unknown, their publication in this volume constitutes an opportunity for scholars to see how this veritable treasure may be of use for biblical studies. David Marcus is Professor of Bible and Masorah at the Jewish Theological Seminary. He authored the book of Ezra–Nehemiah for the new Biblia Hebraica Quinta series being published in Stuttgart by the German Bible Society, and remains a Masorah reviewer for that project. His last two books Scribal Wit: Aramaic Mnemonics in the Leningrad Codex and The Masorah of the Former Prophets in the Leningrad Codex were both published by Gorgias Press in the series Texts and Studies.