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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)

If you have further queries regarding citation styles or reference managers, you may contact us by filling up this question form.

Cite your sources

  • Citing your sources helps you to avoid plagiarism
  • Readers can go back and look at your sources if they would like to follow up or read further.
  • By demonstrating how widely you have researched a topic, your own argument would be more credible.
  • Citations may show yo have 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 have engaged in the topic previously.  



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
    • a reference made within the body of text of an academic essay.
    • add 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 using different citation styles:

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
    • bibliography is a detailed list of works cited in your paper, plus the background readings or other materials that you may have read, but not cited.
    • reference list is a detailed list of references cited in your paper. For example, in APA Style, each in-text citation inserted in the body text must also appear in the reference list, and vice versa.
    • A reference list and a bibliography look similar in that they both contain entries arranged alphabetically, for example, by author, and they include the same basic information. The difference lies in what they contain. Overall, they share similar purposes, which is to help the reader uniquely identify and access each source.
  • Footnotes / Endnotes
    • Some academic disciplines (e.g. 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.
    • This method differs in style from the usual "'author, date'" system but it serves the same purpose, which is to acknowledge the source of ideas, data or quotations without undue interruption to the writing flow.

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.

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.

Citation Generators & Reference Management Software

If you are working with a few references (e.g. less than 20), you can try the following citation builders which are freely available on the web. NUS Libraries, however, do not provide support for any of these tools.

If you work with many references and require a more organised way to manage them, consider using reference management software. For more information, visit this reference management guide developed by NUS Libraries.