The overarching vision of Bt20 is to understand the holistic determination of child and adolescent health and development within Johannesburg-Soweto. This complex study continually impacts on current thinking about youth, and is committed to scientific research that makes a difference. The study documents and explores the socio-economic, socio-political, demographic and nutrition transition that is underway within South Africa and its impact on children and their families. Bt20 research activities cluster into 8 main research themes