Apo or APO may refer to:

• Apo, a god of mountains in Inca mythology
• Abdullah Öcalan, nicknamed "Apo", the leader of the Kurdistan Workers Party
• Acting Pilot Officer, the lowest commissioned officer rank in the Royal Air Force
• Acute Pulmonary Oedema, a medical condition affecting the lungs
• African Political Organization, the first major Coloured political organization in South Africa
• Alpha Phi Omega (ΑΦΩ), a coeducational service fraternity
• Amorphous polycycloolefin, a material used in optical disc substrates
• Apochromat, a lens that has greatly reduced chromatic aberration
• Apolipoprotein, a lipid-binding protein
• Army Post Office, the United States armed forces postal service
• Ausserparlamentarische Opposition (Extraparliamentary Opposition), a German part of the New Left movement
• Asamblea Popular de los Pueblos de Oaxaca

In biology:

• Apo structure, a macromolecule structure without a ligand or co-factor bound as opposed to a holo structure, which refers to an enzyme with its ligand or a co-factor bound.

In business:

• Advanced Planner and Optimizer, a Supply Chain Management computer system by German software giant SAP AG
• Agency purchase order
• American Community Properties Trust, from its AMEX ticker symbol
• Asian Productivity Organization
• The Association for Professional Observers, an association of fisheries observers

In music & entertainment:

• The Armenian Philharmonic Orchestra
• APO Hiking Society, a Filipino singing group
• Authorized Personnel Only, a fictional black-ops division of the CIA on the television series Alias
• Autopilot Off, a pop punk band from Orange County, New York

Places:

• Apo, Nigeria, a Local Government Area in Benue State, Nigeria
• Apo Island in the Philippines
• Apo-eup, a village in Gimcheon, South Korea
• Mount Apo, the Philippines' highest peak
• Apache Point Observatory, New Mexico
• Karaš River, from its ancient Latin name, Apo