Development practitioners are increasingly recognising the value of investing in girls and young women, especially those who live in vulnerable communities whose needs are often invisible in development interventions. This chapter shows the authors' experience using participatory and ethnographic research to inform and shape a girls' health and leadership programme in Sierra Leone. Teenage pregnancy and early motherhood are perceived as critical development challenges in Sierra Leone, which occur primarily due to early sexual initiation and high rates of child marriage. In Sierra Leone, the 14-month pilot project was implemented with the Sierra Leone Family Planning Association, and aimed to involve girls and young women living in poverty and affected by teenage pregnancy in the poorest areas of Freetown. The chapter explains the authors' work to improve the sexual and reproductive health and rights of African women and girls, focusing on the sensitive issues of female genital mutilation, child marriage and related health issues including maternal health and obstetric fistula.