Gender is a social and cultural construct with corresponding hierarchies and inequities that affect health and well-being, making gender an important social determinant of health. Gender roles and stereotypes, including conceptualizations of femininity and masculinity, have consequences for the health and well-being of women and men, including related to caregiving, risk-taking behaviors, mental health, preventive health behaviors, and coping with illness such as cancer. Gender-based stigma and discrimination, including women’s experiences of sexism, women of color’s experiences of gendered racism, and transgender and gender nonconforming individuals’ experiences of stigma and victimization, have harmful effects on these individuals’ well-being, including for mental health outcomes. Gender-based power inequities and violence against women and girls have important implications for health and well-being, including for HIV risk and mental health. Multi-level interventions that address gender norms, roles, and stereotypes, as well as gender-based discrimination and power can help to promote health equity.