Specialist Citation Styles: What Is ACS Referencing?

If you’re editing or proofreading academic writing about chemistry, you may need to know how the ACS referencing system works. But you might not have come across this citation style unless you’re a chemist! To learn the basics, then, check out our guide below.

What Is ACS Referencing?

The “ACS” in “ACS referencing” stands for the American Chemical Society, who developed the system as part of The ACS Style Guide. As with any citation system, this aimed to give writers a clear, consistent approach to citing sources in academic work.

You can find the most recent version of this system in The ACS Guide to Scholarly Communication, which is available online with a subscription.

The tricky thing about ACS, though, is that it offers two distinct citation styles:

• A number–note system, where writers cite sources with numbers in the text that point to an entry in a reference list at the end of the document.
• An author–date system, where writers cite the author’s name and date of publication for sources in brackets within the text, with full source information in a reference list.

We’ll look at both approaches in a bit more detail below.

Number–Note Citations

The ACS actually recommends two versions of number–note referencing. One version uses superscript numbers to indicate citations:

The explosion caused severe damage to the laboratory.¹

And the other uses italicized numbers in brackets:

The explosion caused severe damage to the laboratory (1).

Beyond the presentation of citations, both styles follow the same rules, including:

• Numbering sources sequentially (i.e., the first source an author cites in their work will be “1,” the second source “2,” the third “3,” and so on).
• Using the same number each time a source is cited.

These numbers then point to an entry in the reference list, which should provide full source information. However, individual ACS journals favor one approach over the other. As such, it is worth making sure your client is using the right version for their chosen journal.

Author–Date Citations

The author–date version of ACS style, like other parenthetical referencing systems, requires writers to give the author’s name and date of publication in brackets when citing sources:

The explosion caused severe damage to the laboratory (Harris, 2020).

If the author is already named in the text, though, only the year is cited in brackets:

Harris (2020) reports that the explosion caused severe damage to the laboratory.

When a source has three or more authors, ACS style requires writers to use just the first author’s name in citations, followed by “et al.” (meaning “and others”):

Other experiments have been more controlled (Sunic et al., 2004).

All authors should be named in the accompanying reference list entry, though.

ACS Reference Lists and Formats

ACS reference lists should always contain full publication information for all sources cited, regardless of the system used. But there is a difference in how they’re organized:

• The number–note system lists sources in the order they’re first cited. This is so the position in the reference list matches the citation numbers used in the text.
• The author–date version lists sources alphabetically by author surname. This makes it easy for readers to find the names from the in-text citations.

The exact format for a reference list entry will depend on the source type (e.g., book, journal article, website).However, the ACS does provide some general principles for references:

• Books – References should include the author or editor names, the book title, the publisher, the city of publication, and the year of publication.
• Journal Articles – Include the author names, the abbreviated journal title, the year of publication, the volume number, and the complete page range of the article.
• Other Sources – Provide enough detail for the source to be identified and located.

We’ll admit that last one is unhelpfully vague, but you can find examples of various source types in The ACS Style Guide. See the links above for more information.

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