expert report expert report an expert report is a study written by one or more authorities that states findings and offers opinions. in law, expert reports are generated by expert witnesses offering their opinions on points of controversy in a legal case and are typically sponsored by one side or the other in a litigation in order to support that party's claims. the reports state facts, discuss details, explain reasoning, and justify the experts' conclusions and opinions. in medicine, an expert report is a critical assessment of a medical topic, for example, an independent assessment of the cost–benefit ratio of a particular medical treatment.