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

• University of Illinois Urbana–Champaign in the United States

• User-in-the-loop, a system theoretic paradigm to change user behavior

• User Interface Language, an X11 application language used by Motif

• Uil, a river of Kazakhstan