UI, Ui, or ui may refer to:

• Ui (band), an American post-rock band
• UI (film), an Indian Kannada-language film set for release in 2024
• Upin & Ipin, in which the abbrebiation 'UI' shows in the episode Selamatkan Neo Santara
• Ui Hirasawa, a character from the manga series K-On!
• Ui Miyazaki (born 1981), Japanese voice actress
• Ui Shigure, Japanese illustrator
• Arturo Ui, a fictional character from The Resistible Rise of Arturo Ui by Bertolt Brecht
• Youichi Ui (born 1972), Japanese motorcycle road racer
• Manami Ui (born 1986), Japanese model

• University of Ibadan, Nigeria
• University of Iceland
• University of Idaho, US
• University of Illinois, US
• University of Iloilo, Philippinesee
• University of Indonesia
• University of Innsbruck, Austria
• University of Iowa, US
• Universities Ireland, Northern Ireland
• University of Isfahan, Iran

• The United Illuminating Company, a regional electric distribution company in the northeastern US
• Eurocypria Airlines (IATA airline designator UI)
• Ubiquiti, an American technology company
• Unix International, an open-standard association

• Unit interval (data transmission), also pulse time or signal duration time
• User interface, between human and machine

• Unité internationale, French for International unit, typically used for medication dose
• Unit injector for diesel engines
• Urinary incontinence

• Ui (digraph), used in some writing systems
• Unauthorised information; see Glossary of contract bridge terms#unauth
• Unemployment insurance
• United Ireland, a proposed state
• Universitas Indonesia railway station at the University of Indonesia

• U1 (disambiguation)
• μ_i, the initial magnetic permeability of a material