Custos is the Latin word for guard.

• Custos rotulorum ("keeper of the rolls"), a civic post in parts of the United Kingdom and in Jamaica
• Custos (Franciscans), a religious superior or official in the Franciscan Order
• Custos (Under-sacristan), a Roman Catholic office

• AB Custos, a Swedish investment company
• Custos, a fictional secret organization in the Japanese film series Towa no Quon

• Custos, the latin word for a Direct (music symbol)

The nominative and accusative plural form custodes is used in the proverbial phrase Quis custodiet ipsos custodes?, "Who has custody of the custodians?".