Tetrarch, Tetrarchs, or Tetrarchy may refer to:

• Tetrarchy, the four co-emperors of the Roman Empire instituted by the Emperor Diocletian
• Portrait of the Four Tetrarchs - a sculpture of the four co-emperors of the Roman Empire
• Herodian Tetrarchy, formed by the sons of Herod the Great
• Tetrarch, Military rank#Greek ranks in ancient Greek armies
• Tetrarch (novel), a 2003 novel by Ian Irvine
• Light Tank Mk VII Tetrarch, a British light tank of World War II
• The Tetrarch, a Thoroughbred racehorse
• The Tetrarchs of Ancient Thessaly under Philip II of Macedon
• The Tetrarchs of Galatia in Asia Minor
• Tetrarches, a rank in the Byzantine army
• Tetrarch, a 1981 fantasy novel by Alex Comfort
• Tetrarch (band), a nu metal band from Atlanta, Georgia
• Tetrarchy, a subdivision of the Royal Phalanx in 19th-century Greece
• HMS Tetrarch is the name of the two vessels that have served in the Royal Navy