This work presents to the scholarly world the hitherto unpublished trove of over 500 catchwords that were attached to Masoretic doublet notes in the Leningrad Codex.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. The nature of the catchwords, their purpose, and their relation to other Masoretic notes are described in detail, and suggestions are made how they can be of value to biblical scholars.