Et al.is an abbreviation of the Latin loanphrase et alii, meaning and others. It is similar to etc. (short for et cetera, meaning and the rest), but whereas etc. applies to things, et al. applies to people.
Et al. does not need to be italicized in normal use. It does take a period after the second word, even when it falls in the middle of a sentence. In general, et al. is best reserved for citations and other parenthetical remarks in academic or other types of formal writing. It can sound unnatural when read aloud, so an unabbreviated English equivalent is often better in less formal writing.
The issue of whether to place a comma before et al. is complicated, but you’ll be fine if you treat it as you would the words and others. So when et al. follows a single name (e.g., Tate et al.), it doesn’t need a comma. When it follows more than one name, some publications set et al. apart with a comma, and some don’t. It depends on whether the publication uses the Oxford comma (that is, the last comma in a list—e.g., the one after white in the phrase red, white, and blue).
There are differing ideas about the use of et al., however. If you are writing a paper for a class, you might want to ask your teacher or professor what he or she prefers (if only for the sake of your grade).
This grading system, originally proposed by Daumas-Duport, et al., is simple, objective, and reproducible, and correlates well with survival times. [Journal of Neurosurgery]
As a child I disliked everything about Christopher Robin, from his nanny’s beautiful blue dressing gown on the door to his dim-witted friends Winnie the Pooh, Eeyore, Tigger et al. [Guardian]
Following Hair et. al., the minimum of the item-to-total correlation per item was defined at .50. [Strategic Management in Islamic Finance, Alexander Pock]
Even the recent Gartner report from star analyst Jane Disbrow et al. shows that 61% of their customers have been audited by at least one software vendor. [Forbes]
In Wisconsin, Keefer et al. (1994b) demonstrated that the nuclei of I CM cells from expanded bovine blastocysts were pluripotent. [Laboratory Production of Cattle Embryos, Ian R. Gordon]
Slaying the goliath that is the Los Angeles Galaxy – David Beckham, Landon Donovan et al. – in the 2009 MLS Cup final proved that. [Globe and Mail]