Referencing Guidelines

Citing references in your paper serves two purposes: it allows you to acknowledge the person or people whose data and ideas you are using to support your argument and it provides the information required by the reader of your paper to locate the same sources you used.

Acceptable references

In general, acceptable references for a university research paper includes peer reviewed journal articles and books. Magazines (e.g. Time, Macleans), newspapers (e.g. The Globe and Mail), popular magazines (e.g. National Geographic), and coffee table books are not acceptable sources of information for a research paper. Government publications usually are not peer reviewed, and therefore are often considered unacceptable sources of information. Exceptions can be made when these provide a source of data (statistics). If you are uncertain whether a reference is acceptable, ask your instructor.

Types of papers

Journal articles can be broadly classified into theoretical papers (suggest ideas and hypotheses), primary research papers (present the results of an experiment), and review articles (summarize the current understanding of a topic based on theoretical and research papers). Books generally provide a summary of the information known about a specific topic. Books and review articles will reference primary research papers.


Some journals publish only primary research papers (e.g. Journal of Ecology), whereas others tend to publish summary or review papers (e.g. Bioscience). When you first start researching a topic, it is wise to start with review papers. Spend some time in the library at the beginning of the year; browse the shelves and become acquainted with the available literature in your field of study.


Some authors are associated with specific areas of research; if you have found one paper or book by one author, you will likely find references to many others on a similar topic by the same author.

Where to find references

Start with references provided in the back of your textbook. Go to the library and find other appropriate textbooks, and check the back for relevant references. Obtain some recent review articles in the journals and check the list of references. Use the various abstract services available on CD-ROMs in the library. Talk to your Professor or Teaching Assistant and see whether they can recommend some authors or papers.

Before going to the expense of photocopying many articles, briefly scan the paper to see whether it is suitable for your needs. The purpose and the objectives of the paper will be stated somewhere in the introduction; these should relate to your paper.

Citing references in the text of your paper

Any information that is not general knowledge must be referenced; you must provide sufficient details to allow the reader to find the same facts. When you include dates, statistics, numbers, questionable facts, direct quotations and the ideas of others in your paper, you must indicate the source of this information in a reference.

References should be cited at the appropriate place in the text of your paper using the APA (American Psychological Association) format. The following three sentences provide examples of citing references using the APA format. These examples were extracted from a review article by Margaret Davis that discusses the lags in vegetation response to climate change (Davis 1989).

  1. For example, S.L. Webb (1986) postulates that the passenger pigeon was an effective dispersal agent; this species, formerly very abundant, is now extinct.

    In this example, because the author is being used directly as part of the sentence, the author's name is followed with the year of publication in parentheses.

  2. Tree ring studies show that growth responses of individual trees occur within a year for most species (Brubaker and Cook 1983).

    In this example, the author's name is not used directly in the sentence. However, because this idea was taken from a paper by Brubaker and Cook, they are given credit for it (i.e. it is not an idea that came originally from Davis, the writer of the sentence). Therefore, the source of this idea is cited by placing both the author's name and the year of publication within the parentheses. Note that the period is placed outside the bracket.

  3. On the scale of tens of kilometers, and thousands of years, geographical limits of tree species have tracked past climate changes quite closely (Webb 1986; Prentice 1986; Woods and Davis 1989; Davis et al. 1986a).

    In this example, a list of papers are cited, some of which were written by more than one person; one by two people, and another by three or more. If there are two authors, both are named. However, if there are three or more authors, use only the first author's name and follow that with "et al." to refer to the other authors (underline et al. if you are unable to italicize). Also note that each source is separated by a semi-colon.

    In the case of the reference to "Davis et al. (1986a)", the reason for the letter 'a' is that elsewhere in this same paper the author has cited a reference to a different paper that was also written by Davis and some other authors, and that was published in the same year. The second reference is given as "Davis et al. (1986b)".

    When you list a number of references, as shown in the example above, there must be an underlying logic or rationale for the order of the list. You must be consistent in your ordering of references throughout your paper. The same references could also have been presented as follows:

    • Alphabetical:
      (Davis et al. 1986a; Prentice 1986; Webb 1986; Woods and Davis 1989)

    • Descending date:
      (Woods and Davis 1989; Davis et al. 1986a; Prentice 1986; Webb 1986)

    • Ascending date:
      (Davis et al. 1986a; Prentice 1986; Webb 1986; Woods and Davis 1989)

Other referencing tips

  • Never cite a reference you haven't read; in the rare instance that it is impossible to obtain the original reference, acknowledge it as: "(Smith 1985, cited in Jones 1994)". Avoid doing this.

  • Don't cite class notes. If you wish to include information you learned in a lecture, talk to the instructor, obtain the appropriate reference, read it, and then cite that reference..

  • On very rare occasions you may wish to cite some information that someone told you; this is a personal communication and should be cited as follows: "Little is known about the details of seed dispersal at treeline (David Greene, Personal Communication, 1994)." David Greene is an expert on seed dispersal, and this sentence is the result of a lengthy discussion about seed dispersal at treeline. A personal communication implies that there is no published information that can be cited. It is unlikely that a personal communication will appear in most undergraduate research papers (Honors theses are a possible exception).


Direct quotations should be avoided as much as possible; however, there are instances when a quotation is necessary, such as a precise definition, or the exact wording of a statement. The following rules apply to quotations:

  • Quotations of fewer than three lines occur in the text, enclosed by quotation marks. The reference follows the quote, but occurs before the period.

  • Long quotations of more than three lines should start on a separate line, indented 13 mm (0.5 inch) and single-spaced. Long quotations are not enclosed with quotation marks. The reference occurs at the end of the quotation, after the period.

  • Use double quotation marks for the first order, and single quotation marks for quotations within quotations. Generally, punctuation goes inside quotation marks, but punctuation that is not part of the quoted material goes outside.

  • Ellipses (...) are indicated by exactly three periods inserted between two words, and are used to indicate missing text. They may be either spaced ... or...unspaced, but use one method consistently. If an ellipsis occurs at the end of the sentence, use four periods....

  • Square brackets [like this] are used to add or substitute words in a quotation.

  • When the quotation contains an error, or if you wish to emphasize that you quoted the text exactly, use the term (sic) in parentheses.


The purpose of a "List of References" or "References Cited" section in the paper is to allow the reader to locate the sources you used. The details of the references you used should be listed on a separate page at the end of your paper. This list should include only those sources you actually cited in your paper. The references should be listed alphabetically by author, they should be single spaced, and the title of books and journals should be underlined or italicized. The format followed for citing the references varies hugely between the different books and journals, but is always internally consistent.

Below is an example of a List of References. Note the difference between the way books and journal articles are referenced. In the case of books that are compilations of papers by different authors, cite the author of the particular chapter or paper within the book. Then, as in the example below for Phillips (1974), also provide the pages within the book as well as all the information on the book, such as the editors and the publisher.

List of References

  • Davis, M.B., K.D. Woods, S.L.Webb, and R.P. Futzma. 1986a. Dispersal versus climate: expansion of Fagus and Tsuga into the Upper Great Lakes Region. Vegetatio 67: 93-104.

    The first line of the reference is flush to the left margin, and any additional lines are indented. In the case of a reference with multiple authors, the first author is listed last name first, followed by initials and a comma, and subsequent authors are listed initials first, followed by the last name, and separated by a comma. Vegetatio is the name of the journal, so it is italicized. "Fagus" and "Tsuga" are the Latin names of tree genera, and are also italicized.

  • Odum, E.P. 1971. Fundamentals of Ecology. 3rd ed. Saunders, Philadelphia, 574 pp.

    This is a reference to a textbook. Note that the edition, the publisher, and the place of publication are all included in the reference. It is normal to indicate the total number of pages in the book, in this case, 574 pages.

  • Phillips, J. 1974. Effects of fire in forest and savanna ecosystems of sub-Sahara Africa. Pages 435-481 in T.T. Kozlowski and C.E. Ahlgren (eds), Fire and Ecosystems. Academic Press, New York, 542 pp.

    This reference refers to a paper published in a book. The details of the paper are provided first, then the information about the book, including the editors, title, publisher and place of publication. Since it is a book, the total number of pages in the book is also included.)

  • Webb, S.L. 1986. Potential role of passenger pigeons and other vertebrates in the rapid Holocene migrations of nut trees. Quaternary Research 26: 367-375.

    This is a single-author paper published in a journal. The name of the journal is italicized and followed by the volume number (26), a colon, and the pages on which the article occurs.

Citing Information Obtained from the Internet

For more information about how to reference information obtained on the internet, consult the Purdue University Writing Lab