If your Mac citation library contains multiple records for what may be the same source, compare the records, choose the best metadata, and resolve confirmed duplicates in the reference manager before refreshing the citations in your document. The steps depend on the app: Zotero merges records, while EndNote lets you compare and keep one. First make a recoverable copy of your library, then check whether the records really describe the same work.

What counts as a duplicate citation?

A duplicate is two library records for the same work, often created by importing from more than one database. Similar titles alone do not prove a match: a preprint and its published version, or a print and online edition, may be related records with different publication details. Compare title, authors, year, publication, volume, issue, pages, DOI or ISBN, and item type. Use identifiers as clues, then verify the bibliographic details against the work itself.

A second bibliography entry can also arise because a document contains citations inserted from separate records. Library cleanup and document repair are related but distinct: merging library records does not always update every word-processing citation immediately.

Before changing the library

Close documents that use the library and save your work. Make a backup using your reference manager’s documented backup or export process; these steps vary by app, so do not assume a copied application folder is a valid backup. If a record has attached PDFs, notes, tags, or collection membership, inspect those too. The goal is to retain useful material while removing redundant records.

If two records represent different versions or works, keep both and label or annotate them clearly if your manager supports that. If you cannot determine whether they are the same work, skip the merge and investigate the DOI, publisher page, or full text first.

Reconcile duplicates in Zotero on Mac

In Zotero, select Duplicate Items under the relevant library in the left pane. Choose a candidate group and inspect the highlighted records and their fields in the right pane. Zotero’s duplicate detection uses bibliographic fields, so it can miss records with inconsistent metadata or surface candidates that still need human review. Zotero’s duplicate guidance explains how it identifies and merges candidate items.

For a confirmed duplicate, choose the best record as the master, resolve any field conflicts, and click Merge Items. Merging combines item information and keeps connections such as collections and tags; deleting one record outright can discard those connections. Check attachments and notes after the merge. Work through uncertain groups by skipping them rather than merging on title resemblance alone.

Reconcile duplicates in EndNote on Mac

With the library open, click All References so the search covers the full library. Choose Library > Find Duplicates. EndNote compares records according to the criteria in its duplicate preferences. In EndNote 2025 for Mac, the default is matching reference type, Author, Year, and Title; you can change the fields and choose exact or more lenient matching that ignores spacing and punctuation. EndNote’s duplicate preferences describe these settings.

Review the side-by-side fields. EndNote highlights differences; choose Keep This Record only after checking which version has more accurate or complete information and whether either record is already cited in a paper. That action sends the other record to Trash. Choose Skip to leave both records in place for later review. EndNote’s instructions specifically warn users to check record numbers before deleting a duplicate that may already be cited. Finding Duplicate References in EndNote for Mac

Repair citations in the writing document

After resolving a true duplicate, return to the manuscript and refresh or reformat citations using the citation manager’s word-processing integration. Check the in-text citations and generated bibliography, especially if you had inserted both library records separately. In EndNote, an ambiguous citation can have multiple matching references; its Citation Matches dialog can show the candidates, and you can reinsert the intended reference. EndNote’s formatting guidance explains that citations with other than one match are left unformatted and omitted from the generated bibliography.

Mendeley Reference Manager uses a different flow: its support documentation says version 2.93 and later groups candidates in a Duplicates smart collection, where unwanted references can be deleted. Review each set first, and confirm the document citation remains correct after cleanup. Mendeley’s duplicate instructions

Finish by checking the final bibliography against the manuscript and verifying that each source appears as intended. Keep distinct versions when they matter to your research, and use the manager’s merge or review controls only when the evidence supports treating records as the same work.

Sources