A Work by Two Authors: Name both authors in the signal phrase or in the parentheses each time you cite the work. Use the word "and" between the authors' names within the text and use the ampersand in the parentheses.
Research by Wegener and Petty (1994) supports...
(Wegener & Petty, 1994)
A Work by Three to Five Authors: List all the authors in the signal phrase or in parentheses the first time you cite the source.
(Kernis, Cornell, Sun, Berry, & Harlow, 1993)
In subsequent citations, only use the first author's last name followed by "et al." in the signal phrase or in parentheses.
(Kernis et al., 1993)
NOTE: In et al., et should not be followed by a period.
Six or More Authors: Use the first author's name followed by et al. in the signal phrase or in parentheses.