ISL
- Atatürk Airport
- Cisco Inter-Switch Link
- Ice Hockey Superleague
- Iceland
- Icelandic Sign Language
- Icelandic language
- Illinois Security Lab
- In situ leach
- Independent School League (Illinois)
- Independent School League (New England)
- Independent School League (Washington, D.C. area)
- Independent School League (disambiguation)
- Independent Socialist League
- Independent state legislature theory
- Indian Sign Language
- Indian Super League
- Indonesia Super League
- Institute of State and Law
- Integer set library
- Inter-Switch Link (disambiguation)
- Intercon Security
- International School of Louisiana
- International School of Lusaka
- International School of Luxembourg
- International School of Lyon
- International Service Learning
- International Sign Language
- International Soccer League
- International Socialist League (South Africa)
- International Socialist Left (Germany)
- International Society of the Learning Sciences
- International Sport and Leisure
- International Swimming League
- Interscholastic League of Honolulu
- Iowa and St. Louis Railway
- Iranian Super League (disambiguation)
- Irish Shipping Limited
- Irish Sign Language
- Island Soccer League
- Island line (MTR)
- Isleworth railway station
- Israeli Sign Language
- Italian Sign Language
- Lyapunov stability
- Senglea