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 mental and physical well being. Protecting girls from this multi-dimensional risk requires first understanding how the girls experience vulnerability in their daily lives and developing solutions that are actionable within the community context. 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. This report highlights the project's four phases of action: formative research, intervention design, peer education program, and assessment.