CA4
- CAC CA-4
- Calcium
- California State Route 4
- California's 4th congressional district
- Caproni Ca.4
- Carbonic anhydrase 4
- Central America-4 Border Control Agreement
- Combretastatin A-4
- Hippocampus proper
- Rail transport in Catalonia
- Transport in Barcelona
- USS Pittsburgh (CA-4)
- United States Court of Appeals for the Fourth Circuit