Investing in adolescent girls can bring significant returns. There are currently 1.8 billion young people between the ages of 10 and 24 years globally, and most of them (90%) live in low-and middle-income (LMIC) countries. In order to understand the unique challenges faced by adolescent girls in particular, and effectively deliver on the Agenda 2030’s promise to leave no one behind, robust and disaggregated data collection efforts that capture inequalities faced by adolescents are paramount to drive smart investment.