ACS In-Text Citation: Formats, Rules, and Examples
Your bibliography
0 sourcesACS In Text Citation style points readers to a numbered reference list using one of three formats: superscript numbers, italic numbers in parentheses, or author-date names. Numbers are assigned in order of first appearance and reused for repeat citations.
What are the three ACS in-text citation systems?
ACS lets authors choose among three in-text citation systems, and a paper must use only one throughout. The three are superscript numbers, italic numbers set on the line in parentheses, and the author-date (name-year) format. Journals specify which to use.
The superscript-number system is by far the most common in ACS journals such as Journal of the American Chemical Society. Whichever system you pick, every in-text marker corresponds to a single entry in a reference list at the end of the document. The number or name is the pointer; the full bibliographic detail lives only in that list.
| System | In-text marker | Example sentence |
|---|---|---|
| Superscript number | Raised numeral | The yield increased sharply.⁴ |
| Italic number | (n) on the line | The yield increased sharply (4). |
| Author-date | (Name, Year) | The yield increased sharply (Chen, 2021). |
How do you format ACS superscript numbers?
Assign each source a number the first time it is cited, then reuse that same number for every later citation of the source. Place the superscript numeral immediately after the fact, name, or clause it supports, and set it after commas and periods but before dashes and colons.
You may also cite a reference by placing the italic number in parentheses on the line, for example “the mechanism reported earlier (2).” Both the superscript and the parenthetical italic number draw from the same numbering sequence. The number always ties back to one reference-list entry, formatted like the fully labeled example below.
- Authors — surnames first, initials after; entries separated by semicolons.
- Article title — in roman type, headline case, ending in a period.
- Journal — italic abbreviation, then italic volume and issue and page range.
- Year — set in bold, immediately after the journal abbreviation.
- DOI — full https link, closing the entry.
How do you write ACS author-date citations?
The author-date system places the lead author’s surname and the publication year in parentheses at the citation point, such as “(Chen, 2021).” When the author’s name appears naturally in your sentence, give only the year in parentheses: “Chen and Patel (2021) observed a fourfold rate increase.”
For two authors, join both surnames with “and.” For three or more authors, name the first author followed by “et al.” and the year. The reference list in the author-date system is then arranged alphabetically rather than by order of appearance, which is the reverse of the numeric systems.
| Authors | Parenthetical form | Narrative form |
|---|---|---|
| One | (Chen, 2021) | Chen (2021) found… |
| Two | (Chen and Patel, 2021) | Chen and Patel (2021) found… |
| Three or more | (Chen et al., 2021) | Chen et al. (2021) found… |
How do you cite multiple or repeated sources?
To cite several references at once in the numeric systems, list the numbers together and shorten consecutive runs with an en dash: use “⁴,⁶” for two separate sources and “²⁻⁵” for a continuous span. Separate non-consecutive numbers with commas and no spaces.
Reusing a source is simple: cite it again with the number it was first given, never a new one. In the author-date system, group multiple citations inside one set of parentheses and separate them with semicolons, for example “(Chen, 2021; Anslyn, 2019).” Order those either alphabetically or chronologically, but stay consistent across the whole paper.
- Superscript, separate: Both salts dissolved rapidly.³,⁷
- Superscript, range: Prior syntheses relied on palladium catalysts.¹⁻⁴
- Italic number: These trends match earlier work (3, 7).
- Author-date, grouped: The effect is well documented (Chen, 2021; Grossman, 2019).
What do ACS in-text citations look like with full examples?
The examples below pair a sentence-level marker with the reference-list entry it points to, so you can see both halves of a complete ACS citation. In the reference entries, italics mark the journal abbreviation, volume, or book title, and the year appears in bold.
In textCopper nanoparticles drove the reduction efficiently.⁵
JournalChen, L.; Patel, R. K. Photocatalytic Reduction of CO2 Using Copper Nanoparticles. J. Am. Chem. Soc. 2021, 143 (12), 4567–4578. https://doi.org/10.1021/jacs.1c00123
In textThe stereochemical model is now standard (8).
BookAnslyn, E. V.; Dougherty, D. A. Modern Physical Organic Chemistry; University Science Books: Sausalito, CA, 2006; pp 421–430.
In textReference thermochemical data confirmed the enthalpy values (NIST, 2026).
WebsiteNational Institute of Standards and Technology. Chemistry WebBook. https://webbook.nist.gov/chemistry/ (accessed 2026-07-18).
How accurate is this ACS guide, and what are its limits?
This page reflects the 2020 ACS Guide to Scholarly Communication, the current standard for chemistry publishing. The core rules, superscript numbering in order of appearance and the three permitted systems, are stable across recent ACS guidance and match the house styles of major ACS journals.
The limitation is that individual journals and instructors override defaults. Some journals set superscript numbers before rather than after certain punctuation, use different DOI formatting, or require specific journal-abbreviation forms from the CASSI database. Always confirm your target journal’s author guidelines, because a submission’s local rules outrank any general summary, including this one. When a direct quotation is used, ACS practice is rare but permits adding a page number to the citation.
ACS in-text citation FAQ
What are the three ACS in-text citation styles?
ACS permits superscript numbers, italic numbers in parentheses on the line, and the author-date (name-year) format. A single paper must use only one system throughout, and the superscript-number system is the most widely used.
Where does the superscript number go relative to punctuation?
Place the superscript numeral after commas and periods, but before dashes and colons. Position it directly beside the specific word, name, or clause it supports rather than always parking it at the sentence end.
How do I cite the same source more than once in ACS?
Reuse the number the source received on its first citation. ACS numbering follows order of first appearance, so a repeated source keeps its original number every time and never receives a new one.
How do I cite several references at once?
List the numbers together, separating non-consecutive ones with commas and no spaces (³,⁷) and compressing consecutive runs with an en dash (²⁻⁵). In author-date, group them in one parenthesis separated by semicolons.
Does ACS use author-date in-text citations?
Yes. ACS allows an author-date option giving the surname and year, such as (Chen, 2021). Use “and” for two authors and “et al.” for three or more, and alphabetize the matching reference list.
Which ACS edition should I follow?
Use The ACS Guide to Scholarly Communication, published in 2020, which replaced the 2006 third-edition ACS Style Guide. Still confirm your specific journal’s author guidelines, since they can override the default rules.