IAB may refer to:

• Institute of Architects Bangladesh, a professional organisation for architects in Bangladesh
• Interactive Advertising Bureau, for the online advertising industry
• Internal Affairs Bureau, part of the New York City Police Department, US
• International Agrarian Bureau or Green International, based in Prague, Czech Republic
• Institute of Accountants and Bookkeepers, UK
• International Association of Bryologists, promoting bryology (the study of mosses, liverworts, and hornworts)
• Internet Advertising Bureau, a UK trade association
• Internet Architecture Board, a committee of the Internet Engineering Task Force (IETF)
• Israel Association of Baseball, to promote and develop baseball in Israel

• Isa Air Base, Bahrain
• McConnell Air Force Base (IATA airport code), Wichita, Kansas, US

• IAB meteorite, a group of iron meteorites
• Individual Address Block, in computer networking

• International Accounting Bulletin, a UK accountancy publication