Many adolescent girls in Kenya face considerable risks and vulnerabilities that affect their education status, health, and general well-being. The Adolescent Girls Initiative–Kenya (AGI-K) will deliver multi-sectoral interventions for over 5,000 girls ages 11–14 in two marginalized areas of Kenya: 1) Kibera slums in Nairobi and 2) Wajir County in Northeastern Kenya. Implemented by Plan International in Kibera and Save the Children in Wajir, these interventions will be implemented for two years and will comprise a combination of girl-level, household-level, and community-level interventions. A randomized controlled trial (RCT) will be used to compare the impact of four different packages of interventions, together with their costs, in order to assess if and how intervening in early adolescence will impact girls’ life chances. This report describes the intervention and research design of AGI-K as well as the findings from the baseline survey.