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Citation Styles: Overview

This guide contains information & resources on the commonly used citation styles in NUS such as ACS, AMA, APA, ASA, Chicago/Turabian, Harvard, IEEE, Legal style and MLA.

About this guide

Check with your supervisors, professors, departments, faculty, conference organizers or publishers to find out their preferred citation styles. Once you have determined the style to follow, use it consistently in your paper, bibliography or reference list.

This guide contains information & resources on the following commonly used citation styles:

  • ACS (American Chemical Society)
  • AMA (American Medical Association)
  • APA (American Psychological Association)
  • ASA (American Sociological Association)
  • Chicago/Turabian  
  • Harvard
  • IEEE (Institute of Electrical and Electronics Engineers)
  • Legal Style
  • MLA (Modern Language Association)

An introduction to reference management software is also provided.

If you have further queries regarding citation styles or reference managers, you may contact us here.

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Cite your sources

  • Citing your sources helps you to avoid plagiarism.
  • Readers can go back and look at your sources if they'd like to follow up or read further.                                 
  • By demonstrating how widely you've researched a topic, your own argument ends up being more credible.
  • Citations can show you've considered a wide variety of opinions when forming your own argument. 
  • Citing is standard practice in academic conversations.  Scholars have been debating ideas through written works for years and citing is a way  of respecting those who've engaged in the topic before you. 
  • Citing gives you the opportunity to show off your research abilities!   why cite icon                  

You must cite the source when you...

  • Paraphrase someone's ideas.
  • Mention someone's ideas.
  • Summarize a source.
  • Quote someone's exact words                                                                                
  • Use numerical data, such as statistics.
  • Use an image, such as a picture or a diagram.
  • Use multimedia, such as a video, an animation, or an audio recording.
  • Mention a fact that is not common knowledge.

Citing mainly occurs in these areas of your paper :

  • In-text citation
    • An in-text citation is a reference made within the body of text of an academic essay. Include an in-text citation when you refer to, summarize, paraphrase, or quote from another source. For every in-text citation in your paper, there must be a corresponding entry in your bibliography or reference list.​

Examples of in-text citations:

APA format example: 
The sky is blue (Cottrell, 2013).
ACS format example:
The sky is blue.1
IEEE format example:
The sky is blue [1].
  • Reference list or Bibliography
    • A reference list and a bibliography look very much alike. They both contain entries arranged alphabetically  for example, by author, and they include the same basic information. The difference lies not so much in how they look as in what they contain. The purpose is to help the reader uniquely identify and access each source.

bibliography is a detailed list of works cited in your paper, plus the background readings or other material that you may have read, but not actually cited.

A reference list is the detailed list of references that are cited in your work. For example, in APA Style, each reference cited in text must appear in the reference list, and each entry in the reference list must be cited in text.

  • Footnotes / Endnotes
    • Some academic disciplines (such as history & political science) prefer to use footnotes (notes at the foot of the page) or endnotes (notes at the end of the work) to reference their writing. Although this method differs in style from the usual "'author, date'" system, it serves the same purpose, i.e. to acknowledge the source of ideas, data or quotations without undue interruption to the flow of the writing.

This depends on the following:

  • What type of work you are writing?
    There are different citation styles for different disciplines. For example, when you cite sources in a psychology (APA style) paper you would probably use a different form of citation than you might in a paper for an English (MLA style) class. 
  • ​How you are using the borrowed material?
    ​Identify your sources. If your sources are very important to your ideas, you should mention the author and work in a sentence that introduces your citation. If, however, you are only citing the source to make a minor point, you may consider using parenthetical references, footnotes, or endnotes.
  • The expectations of your instructor!
    Save time by consulting your instructor to determine the form of citation appropriate for your paper.

Adapted from How do I cite sources?,© 2017 Turnitin, LLC.

Academic Integrity is part of the Code of Conduct for NUS Students and NUS Staff. There are several components. Click on the image below to visit the guide in detail, or to re-visit the components.

Variations in Citation Styles

As mentioned, there are various commonly used citation styles so the formatting used in each style is slightly different. The example below illustrates how this particular journal article would be listed in the references section for APA, Chicago, Harvard and IEEE citation styles. Note the differences.

  Authors   Russell Paul Cowburn, Dennis K. Koltsov, Adekunle Olusola Adeyeye, Mark E. Welland, David M. Tricker
  Date   August 1999
  Title   Single-domain circular nanomagnets
  Journal   Physical Review Letters
  Specifics     Volume: 83; Number: 5; Pages: 1024-1045


Cowburn, R. P., Koltsov, D. K., Adeyeye, A. O., Welland, M. E., & Tricker, D. M. (1999). Single-Domain Circular Nanomagnets. Physical Review Letters, 83(5), 1042–1045.


Cowburn, R P, D K Koltsov, A O Adeyeye, M E Welland, and D M Tricker. 1999. “Single-Domain Circular Nanomagnets.” Physical Review Letters 83 (5). American Physical Society: 1042–45.


Cowburn, R. P., Koltsov, D. K., Adeyeye, A. O., Welland, M. E. and Tricker, D. M. (1999) ‘Single-Domain Circular Nanomagnets’, Physical Review Letters. American Physical Society, 83(5), pp. 1042–1045.


[1] R. P. Cowburn, D. K. Koltsov, A. O. Adeyeye, M. E. Welland, and D. M. Tricker, “Single-Domain Circular Nanomagnets,” Phys. Rev. Lett., vol. 83, no. 5, pp. 1042–1045, Aug. 1999.

Two Reference Management Software


EndNote is a software that:

  1. Stores and organizes references found from many sources
  2. Inserts these references into a MSWord document
  3. Automatically formats your references according to a predefined citation style
  4. Secures your research sources as it stays in your local device (if you don't sync
    to the online version)
  5. Recommended for researchers doing biomedical Systematic Review methodology
    as the PRISMA reporting requirements are stringent.
Installation instructions (for NUS staff and students only) and basics of how-to use can be found
at our EndNote Library Guide!



Zotero is a free-to-use bibliographic citation management software that allows you to
save, collect, manage, cite and share research sources. It is a cloud-based software,
so you can access your citations from multiple devices if you sync the Zotero library,
and makes online collaboration easy. Some features deserve to be highlighted:


  1. The Zotero Connector, available as a browser extension in Firefox and Chrome browsers,
    makes it easy to save you citations and capture web pages during the search process.
  2. Its word processor plugin enables integration with MSWord and Google Docs.
  3. Creating a bibliography is quick and straightforward from within the Zotero app. 
  4. Sharing and collaborating your citations with teammates is easy to set up, and your team
    can work on the group library simultaneously
Register for Zotero at, and jump-start with our Zotero Library Guide!  


ZoteroBib is a web-based and simplified version of Zotero software, created by the team behind Zotero. It helps you build a bibliography instantly from any computer or device, without having to create an account, install the software or 'build a library'. It's ideal if you're working on ad-hoc assignments that require less than 20 references.

Use ZoteroBib to:

  1. Add a bibliographic entry using DOI, PMID, ISBN, arXiv ID, or a URLs from Google Books and Amazon
  2. Edit the bibliography and rename the Bibliography heading (if needed)
  3. Change to the desired citation style
  4. Copy the formatted references into your word processor with a click
  5. Export your bibliography
  6. Automatically saves your bibliography as long as you do not close the browser window
  7. Create a link that you can share the bibliography with your team member(s).


A video showing you how to use Zoterobib