Using and citing sources

This page provides information from the NTNU University Library about why and how to cite sources in a paper. The page also explains how to avoid plagiarism.

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Why should you cite the sources you are using?

It is important to cite the sources you have used in your paper or scientific text to show the reader where you found the information, thus ensuring academic integrity.

Correct use of sources shows that you:

  • recognize other authors' work
  • have read literature on your topic
  • place your work in a larger academic context
  • master the technique of naming sources

Correct use of sources also makes the reader capable of:

  • identifying and retrieving the sources you have used

By citing the sources used you avoid plagiarism accusation.

When should you cite your sources?

A large part of what you write will be based on other authors’ ideas, theories, data, findings, etc. When using another author’s work in your own, you must always write where you found this information.

It is not necessary to name sources when writing about something that is publicly known and accepted. For example, it is not necessary to cite sources if you write that Norway voted “No” in the EU referendum in 1994.

How to cite sources

You usually cite sources by

  • in-text reference
  • entry in a reference list

An in-text citation briefly identifies the source. Write the reference’s complete information about the same source in the reference list. The reader should be able to find the reference in the reference list by using the in-text reference, and the information in the reference list should make it possible to find the source. How you write references and the reference list depends on which reference style you choose.

Example (APA style):

cite sources

Reference styles

A reference style has set rules on how to cite sources. Some of the best known styles are APA, Chicago, Harvard and Vancouver.

  • APA style is used in the social sciences, arts and humanities
  • Chicago style is used in the social sciences, arts and humanities.
  • Harvard style is used in the social sciences, technology and natural sciences.
  • Vancouver style is used in medicine and the natural sciences, and sometimes in technology.

There are different traditions for the use of styles in different study programmes. You should check your department's recommendations before writing your paper. Remember, once you have chosen a style, you must use it consistently throughout the entire paper.

Quotations and paraphrasing

Use quotations or indirect quotations (paraphrasing) when you gather information or text from others to use in your own text.


A quotation is a word for word rendering of something somebody else has written. When using quotations, you should mark these in a way that makes it easy for the reader to see what is a quotation and what is your own text. For a quotation, always provide a citation.

Indirect quotations (Paraphrasing)

An indirect quotation (paraphrasing) is a rephrasing of the original text. It may be easier to use paraphrases than quotations because they can be adjusted to fit your own text. A paraphrase can also show that you understand the contents of the original text. When you paraphrase, always provide a citation.

You can find examples of quotations and paraphrasing on the APA style, Chicago style, Harvard style, and Vancouver style pages.

Reference list (Literature list)

A reference list is the same as a literature list. It is a list of all the sources you have referred to in your paper.

  • The APA, Harvard and Chicago (Chicago B) styles use the author-date citation system to cite references in the text, and you write the reference list alphabetically by author’s surname
  • The Vancouver style uses numeric references in the text, and you write the reference list in the order in which the references appear in the text

A bibliography is a separate list of sources you have read but not referred to, and a list of the sources which are relevant to your topic.

What is plagiarism?

Plagiarism means that you publish other people’s work as your own. Plagiarism is regarded as cheating and is strictly forbidden. It is also considered a violation of academic integrity. Plagiarism can result in failing and expulsion from the university indefinitely.

This means that copying from books, articles, etc. or using “copy and paste” from the Internet without referencing is not allowed. You must write where you found the information, that is – referring to the source. Information about academic misconduct at NTNU (only available in Norwegian).

Examples of plagiarism

  • Publishing someone else’s work as your own.
  • Using someone else’s text or ideas in your work without referencing them.
  • Reproducing a text word for word without citing it, and without referencing it.
  • Rewriting (paraphrasing) a text without referencing.
  • Present your own previous work in whole or in part without providing any source (self-plagiarism)

How to avoid plagiarism

To avoid plagiarism, you must cite the sources you used in your work. Learn how to cite sources.

You should keep a good overview of the sources while working on your paper. Write down important information about the sources as you work. If you are writing a paper with many references, you could use a reference management tool to gather and save references.

Checking for plagiarism

Plagiarism detection tools have been developed. NTNU uses the Ouriginal tool.

Reference: Pears, R. and Shields, G. (2016) Cite them right: the essential referencing guide. 10th edn. London: Palgrave.

Reference management tool

Using a reference management tool makes it easier to have an overview of sources you are using in your studies and research. A reference management tool can also help you to create and format citations and reference list in your manuscripts.

A reference management tool can help you to:

  • Collect, organize and retrieve references in your own reference library
  • Insert references in text and create correct citations and reference lists in different reference styles
  • Some reference management tools can find and import full text versions (pdf files) of your references

Different reference management tools

  • The reference management tool EndNote is available for students and employees at NTNU. The library offers courses and guides.

In addition, you can download free reference management tools.

  • BibLaTeX (BibTeX) is a tool you can use with LaTeX. It is specially well suited to text with formulas.
  • Zotero is a free reference management program. Zotero is not as advanced as EndNote, but can be easier to use.
  • EndNote basic is a free web-based version of EndNote. This version does not offer as many functions as the full version of EndNote.

It can be difficult to know what you may share and what sources you may use when writing an assignment. In Norway, it is the Copyright Act (2018) that determines what is legal. The Copyright Act shall protect the interests of those who create works but shall at the same time ensure that others can make use of the works. The Copyright Act gives you the right to quote text from books, articles, websites, etc. provided you state where you have the source from and do not take so much that the creator loses control of the work or income.

Photos, videos, music, etc. can have special challenges. If you want to use an image in your assignment you may

  • use a photo you have taken yourself
  • use an image NTNU has acquired access to (Colourbox)
  • check whether the creator has given permission to use the image (for instance by a Creative Commons license)

There are several types of Creative Commons (cc) licenses. You must examine the rights associated with the cc license for each image you want to use.


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