UST is a three letter acronym that may refer to:
- Hong Kong University of Science and Technology (HKUST)
- Equatorial Guinea Workers' Union
- Northeast Florida Regional Airport in St. Augustine, Florida (IATA Airport Code UST)
- Underground storage tank
- Union of Trade Unions of Chad (Union des Syndicats du Tchad)
- Universal Standard Time
- Universal System Tubeless, a tubeless bicycle tire system developed by Mavic
- University of St. Thomas (Texas) in Houston
- University of St. Thomas (Minnesota) in Twin Cities
- University of Santo Tomas in Manila, Philippines
- UST Growling Tigers, men's varsity team
- University of Science and Technology, universities focus on science and technology
- University of Science and Technology (South Korea), a group of public universities and research institutions
- Tiraspol State University in Moldova
- Unresolved Sexual Tension, the acronym originating with fans of The X-Files
- Unsepttrium (Ust), the predicted last electrically neutral chemical element, with an atomic number of 173
- U.S. Smokeless Tobacco Company, a subsidiary of UST Inc.
- United States of Tara, an American comedy-drama television series
- Ustream website
- .ust, file extension for plain-text Utau voice sequence files
- Uniform Spanning Tree, a mathematical concept; a randomly (uniformly) chosen spanning tree of a graph
- United States Treasury Department of the Treasury of the United States