Long COVID, a prolonged illness after COVID-19, may persist for months after the acute infection and affects at least 65 million individuals worldwide. A puzzling feature of long COVID is that initial disease severity is not an accurate predictor; long COVID frequently occurs in people who had mild-to-moderate COVID cases as well as in younger adults who did not require respiratory support or intensive care. Patients with long COVID should be managed by clinicians who have experience treating this troublesome disorder. Early treatment is essential; the response to treatment will likely be attenuated when treatment is delayed.