An expert report is a study written by one or more experts that states findings and offers opinions.

In law, expert reports are generated by expert witness

Expert witness

An expert witness, professional witness or judicial expert is a witness, who by virtue of education, training, skill, or experience, is believed to have expertise and specialised knowledge in a particular subject beyond that of the average person, sufficient that others may officially and legally...

es 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.