Despite wide acceptance of the stereotype that women apologize more readily than men, there is little systematic evidence to support this stereotype or its supposed bases. In the present research, I explored whether gender differences in apology behaviour occur and, if so, why they occur. In Study 1, I used daily diaries to assess everyday apologies and found that women indeed apologized more frequently than men did. I found no difference in the proportion of offenses for which men and women apologized, however, suggesting that women may apologize more often than men do because they have a lower threshold for what constitutes offensive behaviour. In Studies 2 and 5, I replicated a gender difference in apology behaviour using hypothetical offenses and obtained evidence that this difference is mediated by different judgments of offense severity. In Study 3, I adapted a signal detection paradigm and demonstrated that women exhibit a more liberal response bias in the direction of remembering an apology. In Study 4, I found that women and men similarly associate apologies with positive outcomes, and that only women endorse the stereotype that women apologize more often than men do. Finally, in Study 6, I conducted a daily diary study with romantic couples and found that, as in Study 1, women and men apologized for a similar proportion of the offenses they reported. Together, these studies suggest that a gender difference in apology frequency is caused by different judgments of severity rather than by a difference in willingness to apologize.