As we tackle the challenge of achieving gender equity in education, an immediate question arises: What about gender differences? Are boys more aggressive than girls and does that have an impact on interactions in the classroom and on the playground? Do girls lack mathematical ability and should we therefore kindly allow them to pursue less demanding mathematics courses? Are girls better able to control their motor activity, and, if so, does this give them an advantage in the classroom? In this chapter we review large bodies of evidence regarding whether there are gender differences in domains such as abilities and psychosocial characteristics (e.g., aggression, self-esteem). Then we consider the possible biological and sociocultural forces that may shape existing gender differences. First, though, we consider some overarching methodological issues in research on gender differences.