After six months of development and testing, I am delighted to announce a major update to the Citation Style Language (CSL) styles for the Chicago Manual of Style, available via the Zotero Style Repository. This rewrite is based on a close section-by-section reading of the 18th edition, significantly expanding the styles’ ability to process the information that CSL can collect. The styles can now produce sensible results for nearly every section of the Manual.

For full technical details, see the notes on changes by section available via GitHub.

Main updates from the 17th to 18th edition

See Chicago’s What’s New in the 18th Edition page for a list of changes. Key differences for citations include:

• Author limits: Up to six authors now appear in bibliographies, and up to two in notes or in-text citations accompanied by bibliographies. Notes-only styles differ from notes with bibliographies to accommodate a larger number of authors.
• Shortened notes: Subsequent citations of the same work are now shortened to author–title notes by default; other options include author-only, title-only, and “Ibid.”
• Journal dates: Months or seasons now appear in fewer circumstances, and not at all if there is a volume and issue, meaning that Chicago's critique of Zotero's date display is no longer a problem. The styles also now support ahead-of-print articles, supplements, special issues, and preprints.
• Books: The place of publication is no longer required, and page ranges are optional for book chapters. Use one of the "classic" variants available on the repository to retain these features.
• Bibliographies: Chicago no longer recommends the use of 3-em dashes, preferring to repeat the author’s name. The "classic" variants retain this feature.

The styles also include new or improved support for annotated bibliographies, database and dataset citations, classical and medieval works, audiovisual sources, legal documents, and many other categories.

Expanded variant coverage

The new CSL styles implement more than thirty official Chicago variants. There are four basic systems: in addition to the notes and bibliography and author–date systems, the Manual allows shortened author–title notes and notes without a bibliography. It also gives authors and editors leeway in many smaller details, such as the presentation of references without URLs.

Variants from previous editions that the 18th edition still allows have been grouped into “classic” legacy variants (not an official Chicago term).

Working with the new styles

The styles are designed to match the examples in Chicago’s Citation Quick Guide and the full chapter 14 examples (freely searchable without a subscription). You can explore the variables that each citation type uses through the Zotero Test Items Library. Search for a CMOS section number to see examples encoded from it.

Suppose that you wish to know how to cite a review correctly: Chicago has written a post on the difficulties that this type of citation presents. By searching the CMOS website, you can learn that the Manual covers this topic especially in 14.100 and 14.101. Searching for 14.100 in the Test Items Library will show several examples encoded from this section. In Zotero for desktop, it is also possible to add a Rights column to the display and sort by this to see the examples in the order of the Manual's categories, allowing you to see all the relevant examples from 14.100–102 together. This is especially valuable for citations that rely heavily on the Extra field.

New fields in future Zotero updates

These styles aim to support the full CSL specification. Although Zotero does not yet expose all CSL variables as fields in its interface, this implementation ensures that as new fields are added, Chicago styles will be able to take full advantage of them. For now, you can enter any CSL variable manually via the Extra field. As Zotero adds additional fields, these styles will immediately be able to do something useful with them.

Supporting CSL development

CSL is a volunteer-run, open-source project separate from Zotero. If the Chicago styles support your work, you might consider:

• sponsoring the CSL styles repository on GitHub;
• giving to the Bodleian Libraries, University of Oxford, without which none of my work would be possible;
• taking out a Zotero storage subscription, which sustains the development of the citation manager we all love.

Thanks are due to @bwiernik (whose APA styles provided the foundation for the new Chicago styles) and @adamsmith for guidance. I am especially appreciative of the CMOS staff members who saved me from misinterpreting several sections by answering my queries (but they have not reviewed the implementation as a whole).