Poseidon may refer to:

• Poseidon, the god of the sea in Greek mythology.
• The Poseidon missile.
• The Poseidon drowning detection system.
• The Poseidon bubble, a stock market bubble.
• The asteroid 4341 Poseidon .
• Poseidon, an alternate name for Pasiphaë, a moon of Jupiter.
• HMS Poseidon , a P-class submarine of the Royal Navy.
• Poseidon for UML, UML software.