Custos is the Latin word for guard.
- Custos rotulorum, keeper of the rolls
- Custos (Franciscans)
- Custos (Under-sacristan)
- In Jamaica, it is the title for The Queen's representative in a Parish
- AB Custos, a Swedish investment company
In Musical Notation, the Custos is a symbol which indicates the pitch of the next note on the next line.
The nominative and accusative plural form custodes is well known from the proverbial phrase Quis custodiet ipsos custodes?, "Who has custody of the custodians?", meaning "Who guards the guards?" or "Who watches the watchmen?".