Citing Sources

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What is a citation?

A citation provides enough information to enable a reader to find the same original source material. Typically, this will include author, title of text, date of publication, place of publication, and publisher. Try out Columbia University Library's Citation Finder, which allows you to use citation information to locate the full-text source material. For research help, watch the modules in the From Books to Bytes: Navigating the Research Ecosystem series, which provides students with resources that define the research cycle, give practical strategies, and guide students through the vast resources available to them at Columbia.

When to Cite Sources

You must cite all sources (both texts and images) that have directly or indirectly contributed to your analysis, synthesis, and/or argument in the work you submit.


You should quote your sources when it is important to convey the original author’s precise words.

  • If you use the exact text – words, phrases, sentences – you must enclose them in quotation marks and cite.
  • Short quotes – words and phrases – can be embedded into the text you write. Longer quotes – sentences and paragraphs – should be indented and separated from your words.


If you rewrite the original text in your own words, you must cite the source.


If you summarize the argument or data of another author, you must cite the source.


You must cite any text you read that helped you think about your paper even if you do not reference it directly in the text of your paper.

If a person assisted you in clarifying your thoughts – either in conversation or email correspondence – you must cite this source.

One way might be to acknowledge in a footnote connected to your paper’s title or opening sentence your indebtedness to a book or person (noting the date(s) of any relevant conversation or correspondence). Alternatively, for a more significant piece of work – such as an independent study or senior thesis – you can include a paragraph of acknowledgements, noting the range of assistance you received from many people.

Common Knowledge

Common knowledge is information that a reader can reasonably be expected to know. It does not need to be cited.

  • For example, “Barack Obama, the former President of the United States, was a student of Columbia College” can be considered to be common knowledge and does not need to be referenced.

However, common knowledge does not include opinion.

  • For example, you might agree with the statement “Columbia College is the best college” – but this is an opinion, not common knowledge and to make this case you would have to cite sources and data that support the supposition.

You should therefore be careful in the assumptions that you make in assessing what might be considered common knowledge.

Moreover, what might be common knowledge in one discipline might not be common knowledge in another discipline. It is important, then, to learn from your instructor the expectations for citing common knowledge in any given class.

If in any doubt, err on the side of caution and cite your source.

How to Cite Sources

Learning to cite correctly can be challenging. There are many different citation styles, which are often discipline- or division-specific. You should seek guidance from your instructor or Teaching Assistant to ensure that you understand the citation expectations for any given class.

An invaluable resource is Charles Lipson’s book, Doing Honest Work in College: How to Prepare Citations, Avoid Plagiarism, and Achieve Real Academic Success,  Published in 2008 by University of Chicago Press, this book is available through Columbia University Libraries online catalog CLIO

Another great book on writing to check out is, How Scholars Write by Aaron Ritzenberg, Senior Lecturer in the Department of English and Comparative Literature at Columbia University and Sue Mendelsohn, Senior Lecturer in the Department of English and Comparative Literature at Columbia University, where she serves as Associate Director of the Undergraduate Writing Program and Director of the Writing Center.

In addition, the Librarians in Butler Library, can help you create bibliographies and cite sources using a variety of citation styles and software, and can also help you understand ethical research practices with proper citations. Each semester at Butler Library there are a series of ongoing citation management workshops that teach students how to use Zotero.

The University also provides access to TurnitIn via this request through Student Conduct. Also with ChatGPT and other AI generative software there are now some guidance on how to cite using MLA guidelines.

The most common citation styles are:


Modern Language Association (MLA)

MLA: Formatting a Research Paper


Mathematics and Science

American Chemical Society (ACS) – Chemical Sciences

American Institute of Physics (AIP) - Astronomy, Astrophysics, and Physics

Council of Science Editors (CSE) – Biological Sciences

American Mathematical Society (AMS) - Mathematics

American Society of Mechanical Engineers (ASME) - Mechanical Engineering

Institute of Electrical and Electronics Engineers (IEEE) - Electrical Engineering

American Society of Civil Engineers (ASCE) - Civil Engineering

Association for Computing Machinery - Computer Science


Social Sciences

American Anthropological Association (AAA) – Anthropology & Ethnography

American Psychological Association (APA) – Social Sciences; Academic Writer, Psychology, Education

Chicago Manual of Style – History, Economics, Business, & Fine Arts

American Sociological Association (ASA) - Sociology




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