et al. stands for 'and others' and it should be used in your in-text citations only, to indicate that a work has multiple authors. In your reference list at the end of your work, you should include all of the authors.
It should only be used if the source you are citing has four or more authors (ie more than three). Where a source has one, two or three authors, you should name them all in both your in-text citation and your reference.
et al. should always be written in italics, with a full stop at the end of al.
Previously, if you were a student at St George's, you were required to use et al. in both your citation and your reference list, so this is a change.
Find some examples of the correct use below:
You should use Davey et al., 2015 in your citation but list all of the authors in your reference list. For example: Citation: Davey et al. (2015) discuss the mechanisms of antibacterial drugs....
Reference:
Davey, P., Wilcox, M.H, Irving, W. and Thwaites, G. (2015) Antimicrobial chemotherapy. 7th edn. Oxford: Oxford University Press.
You should use Glavin et al., 2021 in your citation but list all of the authors in your reference list. For example:
Citation: Chronotype is a biological factor that affects sleep (Glavin et al., 2021, p.2637).
Reference:
Glavin, E.E., Ceneus, M., Chanowitz, M., Kantillerakis, J., Mendelow, E., Mosquera, J. and Spaeth, A.M. (2021) 'Relationships between sleep, exercise timing, and chronograph in young adults' Journal of Health Psychology, 26(13), pp. 2636-2647.