I4, i4, I 4 or I-4 may be:
- I4 engine, a designation for an inline-4 piston engine
- I-4 satellite
- HIJMS I-4, a World War II Imperial Japanese Navy J1 type submarine
- LB&SCR I4 class, a British LB&SCR locomotive
- Tupolev I-4, a 1927 Soviet aircraft
- iPhone 4, a smartphone released by Apple Inc. in 2010
- Interstate 4, a Florida highway
- Interstate Airlines IATA airline designator
- International Information Integrity Institute (I-4), a membership-driven program established in 1986 by SRI International, focused on security-related issues and solutions
- i4, an integer in XML-RPC
- I 4, a Swedish regimental designation (4th Infantry Regiment) that has been used by the following units:
- I-4: Loafing and Camouflage, a Greek film
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