Globally, girls and young women are more likely to be hiV-positive than their male peers, due in large part to an array of gender inequalities that negatively impact their their mental and physical well being. The International Center for Research on Women (ICRW) and Taasisi ya Maendeleo Shirikishi Arusha (TAMASHA), in collaboration with Pact Tanzania, developed a participatory research and action project (Vitu Newala) that aimed to both understand and respond to girls’ HIV-related vulnerabilities. The project was conducted in Newala, one of the least developed and poorly resourced districts of Tanzania. The formative research documented in this report highlights four key sources and root causes of girls’ vulnerabilities: harmful gender norms, erosion of the social fabric, exploitative and early sex, and limited communication and support.