ATTENTION: We are currently in the process of moving to our new website located at
Please make note of this and update your bookmarks accordingly. We apologize for any inconvience.

Citing Sources

Why do I have to cite my sources?
How do I cite a source?
What are the different styles for citing documents?
How do I cite a web page or an electronic resource?

Why do I have to cite my sources?

The primary reason for citing the sources you use in a paper or research project is to give credit to the authors of the works that you are using in your research. A secondary reason is to provide your readers with additional sources for further study, and allow them to put your interpretations into context. 

Failure to properly cite your sources consitutes plagiarism and is a violation of moral and professional ethics.

Plagiarism:   "to steal and pass off (the ideas or words of another) as one's own: use (another's production) without crediting the source: to commit literary theft: present as new and original an idea or product derived from an existing source."

Merriam-Webster Dictionary

Purdue University prohibits "dishonesty in connection with any University activity" and plagiarism is an example of such dishonesty. The Office of the Dean of Students has developed a guide for students on academic integrity, with reference to the University's Regulations Governing Student Conduct. Citing sources appropriately will help to avoid plagiarism and will protect you from any questions about the originality of your thoughts and ideas.

How do I cite a source?

Each type of source (book, article, database, web page, sound recording, etc.) has its own particular format of citation.  The format may also vary depending on which citation style is used.

The basic elements of citations for some common types of sources include:

  • Author
  • Title of book
  • Place of publication
  • Publisher
  • Year of publication
Periodical article:    
  • Author
  • Title of article
  • Periodical name
  • Volume number
  • Issue number (if any)
  • Date of publication
  • Page numbers
Web site:    
  • Author (if provided)
  • Name/title of site
    (or description, such as Home page, if not provided)
  • Name of associated institution or organization (if any)
  • Date of access
  • Electronic address

There are several popular styles of citing documents. Style guides which are available in the Purdue Libraries collections include:

ACS Style Guide (American Chemical Society)

American Medical Association Manual of Style

Chicago Manual of Style (University of Chicago)

Manual for Writers of Term Papers, Theses, and Dissertations (Kate Turabian)

MLA Style Manual and Guide to Scholarly Publishing (Modern Language Association)

Publication Manual of the American Psychological Association

Scientific Style and Format: The CBE Manual for Authors, Editors, and Publishers (Council of Biology Editors)

You may also find web sites -- such as Purdue University´s Online Writing Lab (OWL) or St. Martin's Press Citation Styles -- which will provide information about citing sources using different styles.

Your instructor should give you guidance as to which format(s) are acceptable for your assignment.

How do I cite a web page or an electronic database?

Because electronic resources can be easily altered, they raise additional concerns regarding documentation.  It is important to include in a citation both the date the site or resource was created, as well as the date that you viewed it.

The most recent editions of the above style guides contain information about and examples of citations for electronic resources.

Some web sites that provide information specific to citing electronic sources include:

APA Electronic Reference Format Page

The MLA Style FAQ site

St. Martin's Press Citation Styles
Within the section for each citation style (MLA, APA, Chicago, and CBE) , provides specific examples of how to cite electronic resources.

Purdue University's Online Writing Lab - Documenting Electronic Resources
Good collection of links to resources for APA and MLA citation styles.

Citation Guides for Electronic Documents
Provides a tremendous collection of Web sites on citation styles and a detailed look at citing email messages.