A quarantine is a restriction on the movement of people, animals and goods which is intended to prevent the spread of disease or pests. It is often used in connection to disease and illness, preventing the movement of those who may have been exposed to a communicable disease, yet do not have a confirmed medical diagnosis. It is distinct from medical isolation, in which those confirmed to be infected with a communicable disease are isolated from the healthy population. Quarantine considerations are often one aspect of border control.

The concept of quarantine has been known since biblical times, and is known to have been practised through history in various places. Notable quarantines in modern history include the village of Eyam in 1665 during the bubonic plague outbreak in England; East Samoa during the 1918 flu pandemic; the Diphtheria outbreak during the 1925 serum run to Nome, the 1972 Yugoslav smallpox outbreak, the SARS pandemic, the Ebola pandemic and extensive quarantines applied throughout the world during the COVID-19 pandemic since 2020.

Ethical and practical considerations need to be considered when applying quarantine to people. Practice differs from country to country; in some countries, quarantine is just one of many measures governed by legislation relating to the broader concept of biosecurity; for example, Australian biosecurity is governed by the single overarching Biosecurity Act 2015.