Ordo (Latin "order, rank, class") may refer to:
- A musical phrase constructed from one or more statements of a rhythmic mode pattern and ending in a rest
- Ordo (palace) (Orda or Horde), is a nomadic palace for the Mongol aristocrats and the Turkic rulers
- Order (biology), in the taxonomy of organisms
- Ordo Recitandi: The Ordo gives complete details of the celebration of the Eucharist and the Liturgy of the Hours, beginning with the first Sunday of Advent
- The Inquisition from Warhammer 40,000 has three main ordines:The Ordo Malleus,The Ordo Hereticus and The Ordo Xenos
- Monastic order
- Ordo Templi Orientis, an organization dedicated to the religious philosophy of Thelema
- The scholarly economic/political science journal ORDO, The Annual Review of Economic and Social Order
- Canderous Ordo, a fictional character in the Star Wars video games Star Wars: Knights of the Old Republic and Star Wars: Knights of the Old Republic II: The Sith Lords
- A fictional encryption program from the book Cryptonomicon, by Neal Stephenson
- Novus ordo seclorum which appears on the reverse of the Great Seal of the United States
- Ordo Missae, the order (regulation) of the Eucharist in the Roman Rite of the Catholic Church