The Epstein-Barr virus (EBV), also called Human herpesvirus 4 (HHV-4), is a virus of the herpes family (which includes Herpes simplex virus and Cytomegalovirus), and is one of the most common viruses in humans. Most people become infected with EBV, which is often asymptomatic but commonly causes infectious mononucleosis.

EBV is named after Michael Epstein and Yvonne Barr, who together with Bert Achong, discovered the virus in 1964.