The document summarizes lessons learned from establishing the first social impact bond (SIB) in Estonia in 2015. The Good Deed Foundation implemented the SIB to reduce recidivism among 14-17 year olds using aggression replacement training. Key lessons included selecting an intervention with available data and multi-actor competencies; considering service provider capacity, impact measurement experience, and sustainability; structuring investments for low volumes and high risk; establishing a detailed impact framework; and developing early legal and procurement frameworks for multi-year commitments.