Driving a multi-sector collaboration for countering online child sexual exploitation.To create systemic change at a societal level and solve a wicked problem like online sexual exploitation of children (OSEC), we need to understand and consider all people involved in the ecosystem. This talk explores the required sensitivity and strength in doing so: how robust research and strategic design can lead to responsible investment and ecosystem mobilisation; and how it helped a newly set up NFP organisation and manager of the Child Protection Fund (CPF) define, refine and maximise social impact.