The 9th International Expert Symposium on Accident Research (ESAR) took place online on 23-24 March 2021. ESAR was organised by the Medical School of Hannover and it was a platform for exchanges of information on accident research issues. The conference focused on accident research general, accident causation, pre-crash analysis, accident reconstruction, new data sources for accident research such as video observation and EDR, injuries, regulation and consumer information.