The Epstein-Barr virus (EBV) was discovered in 1964. At the time, the very idea of a virus underlying a cancer was revolutionary. Cancer is, after all, not catching. Even now, the idea of a virus causing cancer surprises many people. But Epstein-Barr, named after its discoverers, Sir Anthony Epstein and Dr Yvonne Barr, is fascinating for other reasons, too. Almost everyone carries it, yet it is only under certain circumstances that it produces disease.