UIL may mean:

• UIL Holdings Corporation, a natural gas company based in Connecticut, U.S.
• UNESCO Institute for Lifelong Learning, a United Nations educational centre
• Unione Italiana del Lavoro, the Italian Labour Union
• United International Airlines, ICAO designator of a Serbian cargo airline
• United Irish League, a nationalist political party in Ireland from 1898 through the 1920s
• University Interscholastic League, the governing body for public school interscholastic activities in the US state of Texas
• User-in-the-loop, a system theoretic paradigm to change user behavior
• User Interface Language, an X11 application language used by Motif
• Uil River, a river of Kazakhstan