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American Chemical Society (ACS) Citation Style Guide


This guide is based on the new 2020 edition of the ACS Guide to Scholarly Communication. It will assist you by providing examples for:

  • formatting in-text citations
  • formatting a reference list
  • structuring your paper for course work

Not all of your questions will be answered here, as we have focused on commonly used sources and formatting.

For more detailed information and other examples:

  • consult the full ACS Guide to Scholarly Communication (link below)
  • contact your subject librarian

Why and When we Cite

Why we cite

When we write a paper, we gather background information and build arguments drawing on the work, knowledge, ideas, expressions, and reportings of others.

This information is found in many places -- journal articles, books, YouTube videos, blogs, maybe even in an email. Whatever the source, we are required to acknowledge who or what that source is when we refer to the work in our own.

We may refer to another person's work for many reasons. These include:

  • setting the stage for your position on a topic;
  • demonstrating support for an idea by another person;
  • demonstrating an opposing viewpoint.

When we cite

Citations create necessary links, directing your reader to the source you're crediting. We make an in-text citation that links to our reference list at the end of our document, which then links to the original source.

For this reason, when we talk about citations, we're talking about two different instances, once in the body of our text -- In-text citations -- once at the end of our text -- the reference list.

How we cite

When using ACS, the in-text citations are commonly denoted with a superscript marker (raised number) at the end of the sentence or piece of information that is being pulled from the reference. The superscript number is repeated for each time that same reference is used, and then it is tied to the same number in the reference list for that full citation

This new edition of the ACS Guide does outline additional ways of creating in-text referencing. Superscripts are still a preferred method, but parenthetical referencing and author-date referencing are other options (see section 4.3.2). 

Terms and Definitions

DOI. A digital object identifier, a persistent and unique number set to link back to that one resource located online. 

URL. A uniform resource locator, a link to a resource located online. It can be updated over time and often not considered to be persistent, although examples of permanent URLs do exist. 

Aggregator databases. These include most databases available through the library, where materials are not uniquely located and may be available through multiple databases (e.g. Web of Science, PsycINFO, Academic Search Complete, Google Scholar, ProQuest eBook Central, etc.). If you retrieve an article or an e-book from an aggregator database, you are required to note this in your reference when using ACS (see section 4.3.5). 

Publisher databases. These are another example of databases available through the library, where materials are being offered full-text through the journal's website offered by the publisher (e.g. ScienceDirect (Elsevier), Cambridge Core (Cambridge), ACS Publications (ACS), etc.). If you retrieve an article or an e-book from a publisher database, you do not have to include this in your reference when using ACS (see section 4.3.5). 

Article number. If an online journal article does not have page numbers, it often has an article number instead. You can list this as you would page numbers for the article. 

Reference List

Some general rules to consider when creating your reference list:

  • Every source used in your in-text citations needs to be listed as part of your reference list
  • Sources appear in order of appearance in the paper, ensuring the number used in-text matches the one in the References list. 
  • Sources appear in the format: number, period, space, and the citation
  • The word References should appear at the top of your reference list, and it should be left-justified and bolded on the page
  • Titles should be written in upper case format, except for transition words that are lower-case (e.g. and, or, the).
  • List all authors in the order that they appear in the source.
  • All subsequent lines in a reference should not be indented. All lines should remain flush to the left-hand margin.

For more, see section 4.3.2 of the ACS Guide of Scholarly Communication.