The purpose of clearly and completely documenting all sources that you use is twofold. Firstly, you need to give credit for all ideas that are not your own to the people or organizations who originally created them. All new scientific discoveries build on the work and ideas of others and citations are the accepted way of respecting those whose work was crucial for your own work to succeed. Secondly, complete citations give credence to your work because a reader can find and check the original source for themselves. Without citations, any claims you make that you can't back up with your own data are questionable.

It is always best to read and cite primary sources rather than secondary sources because this is the only way to make sure you know what the original authors said. However, at times it can be difficult to track down original sources, or, especially when writing lab reports, tight timelines can simply make it too time-consuming to hunt down all the primary articles. If you need to cite a secondary source, make sure you clearly indicate to your audience that you did not read the primary source. You can do this by including "as reviewed in…" if you are citing a review article. If you are citing a study via another primary source include the original studies authors and then "as cited in…". See examples below.

Make sure to check with your instructor before using secondary sources as in some courses, particularly at the upper levels, your instructor may expect you to use primary sources only.

What to include

Include full citations for all resources that are cited in your report. There is actually two parts to citing sources.

  1. Clearly indicate throughout your paper what sources were used for particular points or pieces of information. This is generally referred to as "in-text citations". There are several systems used for in-text citation; in our department we generally expect citations to be done using the "Name-Year" system.
  2. List the references at the end of your document (end references). While there can be some variability as to the order in which the various required components are listed for each citation, the information that must be included is pretty standard.


As recommended by the Council of Science Editors (CSE), biological publications generally follow the National Library of Medicine (NLM) method of referencing. The complete book, Citing Medicine, 2nd edition: The NLM Style Guide for Authors, Editors, and Publishers is available online at the NCBI bookshelf. We will give you some basic guidelines here, but there is no way we can summarize a 26 chapter book. It is your responsibility to find out how to properly cite the sources you have used.

A note on quoting Using direct quotes in science is generally not acceptable. Please see quoting for more information.

In-text citations

Inserting citations parenthetically

Most of your citations should follow this method. Here, the publication is simply included in parentheses following the information that is being cited.

  • Single author - indicate the author's last name and the year of the publication (Author year).
  • Two authors - indicate both authors' last names and the year (Author and Author year).
  • Three or more authors - only indicate the first author's last name, followed by et al. and the year (First Author et al. year). Using "and others" in place of et al. is also acceptable.


(Smith 1999) (Smith and Jones 2000) (Smith et al. 2001) (Smith and others 2001)

Inserting citations where the author(s) is mentioned directly in the text

In this case, the author(s) is mentioned as part of the text and only the publication year is placed in parenthesis.

Note that this type of citation should be used sparingly or not at all. Including names in the text takes up a lot of space and frequently detracts from the point you are trying to make.

  • Single author - "According to Author (year), such and such is true".
  • Two authors - "According to Author and Author (year), such and such is true".
  • Three or more authors - "According to Author et al. (year), such and such is true". It is also acceptable to state: "According to Author and colleagues (year), such and such is true".


According to Smith (1999)… According to Smith and Jones (2000)… According to Smith et al. (2001)… According to Smith and others (2001)…

Citing contributors of a specific part of a book

Some books are collections of articles where each article has its own author. In this case the book usually will have editors listed on the cover (the editors put the book together, but didn't necessarily write any of the articles).
If you only used a specific part/chapter of the book, the in-text citation should include only the author(s) of this part.

Citing sources that do not have an identifiable author

  • First try to find a better source for your information. Most good sources have an author's name associated with them.
  • If you really must use an authorless source (for example a product handbook), DO NOT use anonymous. Use the first word or first few words of the title, followed by an ellipsis (three dots with a space before and after) and the year.


Plasmid DNA binds to the silica column (GeneJET Plasmid … 2011).

Situations where the author, year system is not specific enough

If you have more than one article published in the same year by the same author, more than one author with the same last name, or when organizations (such as a university) as authors, please see the NML guidelines.

Citing secondary sources such as textbooks and review articles

If you cite a secondary source make sure you clearly indicate to your audience that you did not read the primary source. You can do this by including "as reviewed in…" if you are citing a review article. If you are citing a study via another primary source, include the original study's authors and then the words "as cited in…".

Gibberellins were first discovered and extracted from the fungus Gibberella fujikuori in Japan in the 1930s (reviewed in Stowe & Yamaki 1957).

Gibberellin was first shown to promote flowering in Arabidopsis (Langridge 1957 as cited in Evans and Poethig, 1995).

Citing information found on the web

If the web information has an author and a date just follow the same rules as for print materials (where it gets complicated is putting together the end reference information).
Most high-quality science sites tell you how to cite them (you might have to look around a bit).
Online Mendelian Inheritance in ManĀ® (OMIMĀ®) has an FAQ. The FAQ contains instructions for citing the resources.
Tree of Life Web Project specifies how to cite under the "About" menu.

For all other online citation situations, the NML has detailed specifications that are easy to follow.

End references

Only include references that you cited in your research report!

All end references must include enough information to uniquely identify the exact source, and o make it easy to find the original source. For all types of sources you will, at minimum, need the author(s), source title, and date of publication. Other required information will depend on the source and also on the journal format you are following (your instructor may ask you to follow a particular journal's format).

We have listed a few common examples here. For any other source type please see NML.

Journal articles from print sources

1st author (last name, up to 2 initials), 2nd author, etc. until all the authors are listed. Date of publication. Full journal article title (exactly as it appears in the journal). Journal Title (use abbreviated from as indicated by the journal). Volume(Issue): pages.


Gillam EH, O'Shea TJ, Brigham RM. 2011. Non-random patterns of roost emergence in big brown bats, Eptesicus fuscus. J. Mammalogy. 92(6):1253-1260.

Things that can vary (depending on the exact format you are following)

  • Frequently only the year of publication is included.
  • The issue number is not always included.
  • The order of some elements can vary depending on what journal style you are following.
  • Authors are always listed in the order they appear on the article and the 1st author's last name is always listed first, but the order of the first and last names of the remaining authors can be reversed.
  • NML and CSE standards both format the authors' names as shown in the example, but individual journals may have different recommendations.

Journal articles from an online source

To cite journal articles that you have found online, you follow the same format as if you were using the print version, except you must add [Internet] after the journal name to indicate the medium, [date cited] after the publication date, and at the end of the reference add "Available from hyperlink".

If you used the online version of the journal article, you must indicate this in the citation. Don't pretend you used the print version to save time because there can be differences between the two versions (e.g. sometimes printing errors are corrected in the online version).

The citation will look like this:

Gillam EH, O'Shea TJ, Brigham RM. 2011 [Cited Aug. 15, 2012]. Non-random patterns of roost emergence in big brown bats, Eptesicus fuscus. J. Mammalogy [Internet]. 92(6):1253-1260. Available from

Citing an entire book


Author(s)> Book Title. Edition (Ed. ). Place of publication. Publisher. Date. Pagination (total# of pages p.).


Griffiths AJ, Wessler SR, Lewontin RC, Carroll SB. Introduction to Genetic Analysis. 9th ed. New York: W. H. Freeman and Company; 2008. 838p.

Chapters or parts of a book where the entire book has the same author(s)

If you used only a particular part of a book, your end reference should specify what part you used. Start by referencing the book as usual, and then add information about the part.


Griffiths AJ, Wessler SR, Lewontin RC, Carroll SB. Introduction to genetic analysis. 9th ed. New York: W. H. Freeman and Company; 2008. 838p. Chapter 3, Independent assortment of genes; p.89-128.

You can use this format to specifically cite any identifiable portion of a book, such as a section, table, chart, graph, photograph, or an appendix.



Lintott, L. Biology 205 laboratory manual. 6th ed. Regina: University of Regina; 2011. Investigating inheritance in Drosophila melanogaster; p.43-65.

Dietz, HGS. Biology 220 Laboratory Manual. Regina: University of Regina; 2012. How can we use chemicals to control microbial growth?; p.56-58.

Chapters or parts of books with contributing authors

If the book is a collection of parts written by different authors, first give the information for the contribution, then the word In: and then the information for the book.


Wages JM, Zhao X, Katz ED. High-performance liquid chromatography analysis of PCR products. In: Innis MA, Gelfand DH, Sninsky, JJ, editors. PCR Strategies. London: Academic Press; 1995. p.140-153.

Books published by an organization, no identifiable author

If the book is produced by an organization, for example a manual produced by a company, the organization is the author.
Example: This citation references a manual that describes how to use purchased kit.

Thermofisher Scientific. GeneJET plasmid mini-prep kit. Thermofisher Scientific. 2014.

Other online sources (including databases and retrieval systems)

As noted above, most quality science sties will specifically tell you how to cite them (you might have to hunt around the site a bit).
For all other situations, see NLM, in particular the chapters that deal with citing online resources.

If you must use and website for which no author is listed, first make sure it is a reliable source and then use these NLM instructions. Note that your instructor may not allow authorless websites as acceptable resources.


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