• An alternate symbol for the international unit (IU)
• Eurocypria Airlines, IATA airline designator
• Unemployment Insurance
• United Ireland
• Universal indicator
• Universities Ireland
• Unix International
• Unit Injector, a fuel injection technology for diesel engines
• Urinary incontinence
• User interaction
• User interface
• Ui (digraph), a digraph used in some writing systems
• Ui, an ancient Phoenician colony located at the site of modern-day Tripoli in Libya
• Arturo Ui, a fictional character from The Resistible Rise of Arturo Ui by Bertolt Brecht
• Ui (band), an American post-rock band

In education:

• University of Innsbruck
• University of Indonesia
• University of Ibadan, Nigeria
• University of Idaho
• University of Illinois
• University of Iowa

See also

• μ_i, The initial magnetic permeability of a material