The way you refer to a source in your paper is the same for physical and online sources. You need to refer to a source when you cite someone, or when you paraphrase their ideas, data, theory, ... Below you can find concrete examples that show you how to do this in APA style (7th ed.) for the most common types of sources. At the at end of your text you'll include a reference list with all the works you've consulted.

• One author
• Two authors
• Three or more authors
• Multiple authors with the same findings
• Author of a contribution
• No authors

 

One author

The most simple reference is that to one author. The author does not have to be an actual person, sometimes institutions are seen as an author. For this type of reference you put the following information between round brackets:

• last name
• comma (,)
• year of publication

If you mention the author by name in the text, you only mention the year of publication at the end of your sentence between round brackets.

Parenthetical citation

"In forests, components like understorey vegetation are indispensable to ecosystem stability and ecological function" (Wang, 2021).

Narrative citation

Wang (2021) finds that herbs as forest litter help regulate the soil biotic and abiotic environment.

 

Two authors

To refer to a source by two authors, you put the following information between round brackets:

• the last name that is mentioned first in the original publication
• ampersand (&)
• last name 2
• comma (,)
• year of publication

If you mention the authors by name in the text, you only mention the year of publication at the end of your sentence.

Parenthetical citation

"Hyphomycetes are filamentous fungi that reproduce by conidia generally formed aerially on conidiophores arising from the substrate" (Goettel & Inglis, 1997).

Narrative citation

Thanks to their relatively low weight, bats fly more easily, note Dietz & Kiefer (2017).

 

Three or more authors

To refer to a source by three or more authors, you put the following information between round brackets:

• the last name that is mentioned first in the original publication
• the abbreviation "et al."
• comma (,)
• year of publication

If you mention the authors by name in the text, you add "et al." after the first last name and mention the year of publication at the end of your sentence between round brackets.

Parenthetical citation

"Rozella has a small body without a cell wall, which branches within the host and makes two types of sporangia: zoosporangia, which produce zoospores with posterior flagella that swim from the parent to find new hosts, and resistant sporangia, around which a thick cell wall develops to ensure persistence long after the host has died and decayed" (Stajich et al., 2009).

Narrative citation

Stajich et al. (2009) reiterate that we know next to nothing about the reproduction of Rozella.

 

More authors with the same findings

If you want to refer to the same findings or theories from different authors, you mention all authors within one set of round brackets, separated by a semicolon (;):

• last name
• comma (,)
• year of publication
• semicolon (;)
• last name
• comma (,)
• year of publication

Narrative citation

Child mortality rates are high with pandas. Therefore, breeding in captivity can be seen as a necessary measure (Laidler & Laidler, 1992; Catton, 1990).

 

Author of a contribution

If you want to refer in your text to an author who contributed to a book, but who did not write the entire book (e.g. an essay collection), you refer to the text of the contribution. In the reference list, you include a reference to the entire work. The reference in the text will be the following information between round brackets:

• last name of the author (not the editor)
• comma (,)
• year of publication.

If you mention the author by name in the text, you only mention the year of publication at the end of your sentence between round brackets.

Narrative citations from The ostrich : biology, production and health, edited by D. C. Deeming

When breeding the youngest ostrich chicks, it is best to control the temperature at 30°C and drop it slightly each day, according to Verwoerd et al. (1999).

Intensive selection and interbreeding with wild ostriches causes a better feather quality in South-Africa (Petitte & Davis, 1999).

 

No author

If a work doesn't have an author (this can be a person or an institution), you mention (part of) the title of the publication. Put the following between round brackets:

• the first (few) words of the title, except articles or numbers
• comma (,)
• year of publication

Narrative citation

In terms of environmental protection, the protection of plants has known the most improvement in Germany of the 1990s (Landwirtschaft, 2002).

American Psychological Association. (2020). Publication manual of the American Psychological Association (7th ed.). https://doi.org/10.1037/0000165-000