Two decades of research have shown that challenging harmful codes of masculinity and femininity and improving gender equity is a major key to improving life outcomes for at-risk youth, like those who are of color or LGBTQ. For instance, young men who buy into rigid codes of manhood as defined by strength, aggression, sexual prowess, and emotional toughness have earlier sex, more sexual partners, and lower condom use. They're more likely to view pregnancy as a sign of manhood, to see sex as adversarial, and to believe that control of a female partner -- with force if necessary -- is central to maintaining their masculinity. Agencies like PEPFAR, USAID, UNAIDS, and WHO -- and leading NGOs like CARE, EngenderHealth, ICRW, Planned Parenthood, and Population Council -- have all implemented gender transformative initiatives and found them effective. Yet, as Dr. Hortensia Amaro first observed in 1995, the US still pursues better life outcomes for at-risk youth "in a gender vacuum." This accessible overview introduces the basic language, concepts, and findings about gender norms and their impact on reproductive health and partner violence.