IOL may mean:

• Iol, an ancient city in Algeria, now Cherchell
• Independent Online (South Africa), news website
• Institute of Linguists, UK, now Chartered Institute of Linguists
• International Linguistics Olympiad, an International Science Olympiad
• Intraocular lens, eye implant
• Ireland On-Line, a former internet service provider (ISP) in Ireland
• The University of New Hampshire InterOperability Laboratory (UNH-IOL), for networking testing

• Bana cathedral
• Banach-Alaoglu theorem
• Banach analytic Lie group
• Banach analytic manifold
• Banach bundle (non-commutative geometry)
• Banach contraction mapping principle
• Banach contraction mapping theorem
• Banach contraction principle
• Banachek
• Banachiewicza
• Banach match problem
• Banach-Mazur compactum
• Banach-Mazur distance
• Banach-Mazur theorem
• Banach's Contraction Principle
• Banach's contraction principle
• Banach Space
• Banach space of analytic functions with infinite-dimensional domains
• Banach Spaces
• Banach-Stone theorem
• Banach-Tarksi paradox
• Banach Tarski
• Banach Tarski paradox
• Banach Tarski Paradox
• Banach-Tarski Paradox