On Wednesday 15 January 2020 the OECD hosted a second webinar in the series of Adverse Outcome Pathways (AOPs). It focused on the importance of weight of evidence in the process of developing AOPs, the types and lines of evidences assembled, examples demonstrating the lines of evidence and understanding why quantitative AOPs are developed. The AOP framework is a collaborative tool that applies an innovative approach for collecting mechanistic knowledge from various sources that can eventually support chemical safety assessment. Magda Sachana from the OECD Environment Directorate introduced the presenters and scope of the webinar.