Adolescent girls face distinct challenges that require tailored and girl-centered responses. This brief draws on the knowledge of program implementers and researchers who work on community-based girl group (CBGG) programs (often called "safe spaces") in various low- and middle-income settings and the US. It summarizes emerging lessons and insights on CBGGs, emphasizing the vital role that mentors play in this group-based model. The evidence emphasizes the importance of providing mentors with training, supervision, compensation, solidarity, and opportunities to build their own networks.