Gender differences are ubiquitous in the social psychological literature as there is an intense belief that men and women differ in most behaviour. The assumption is that the difference is either essential (biological differences) or learned (social differences) and can interact to produce the differences we see today. However, even with researchers' interest in revealing gender differences, studies have been conducted rather atheoretically and sometimes produce inconsistent results. The present thesis addresses prejudice -an area of social behaviour proposed by some researchers to be gendered in nature but currently lacking in systematic review and empirical studies. The present thesis will examine multiple theories for gender differences in prejudice with a meta-analysis and three lab studies assessing the biological and social components to any effect.At first glance, there appears to be consistent evidence of gender differences. For example, women have reported more favourable attitudes than men on social issues such as desegregated neighbourhoods and funding for public schools (Hughes & Tuch, 2003). In comparison, surveys have found that men reported higher levels of xenophobia, endorsement of White superiority, and racism compared to women (Ekehammar & Sidanius, 1982;Sidanius, Ekehammar, & Ross, 1979).However, meta-analyses have demonstrated that gender effects can vary across different operational definitions of prejudice (Hughes & Tuch, 2003) and that overall there is more evidence for gender similarities than differences (Hyde, 1984).This thesis therefore begins with the report of a meta-analysis (Study 1) that provides a comprehensive review of the literature assessing whether gender differences exist in the psychological literature of prejudice. The meta-analysis covered over 50 years of research and included 772 datasets. Across all studies, a small effect (r = .101) of gender was found, with men demonstrating more prejudice than women. The size of this effect, however, was moderated by several variables, including the measure of prejudice, social category of the outgroup, and gender of the target. My analyses also uncovered no instance where women demonstrated more prejudice than men. The results demonstrate that prejudice is somewhat influenced by gender but the small effect size indicates that other variables may play a larger role.Informed by the results of this meta-analysis, the following studies were designed to understand the underlying mechanisms of this gendered phenomenon. Study 2 investigated whether the effect can be explained from a biological perspective, specifically hormonal differences. The study tested basal levels of testosterone, measured via a saliva sample, and its interaction with cortisol to also assess a dual hormones hypothesis. In addition, I examined the role of prenatal testosterone exposure through the measurement of digit ratio (2D:4D) and facial width to height ratio (fWHR). Results revealed no significant association between gender, testosterone, cortisol, or...