IAB may refer to:
Organisations 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) Islami Andolan Bangladesh, political party in Bangladesh Israel Association of Baseball, to promote and develop baseball in Israel
Air force bases Isa Air Base, Bahrain McConnell Air Force Base (IATA airport code), Wichita, Kansas, US
Science and technology IAB meteorite, a group of iron meteorites Individual Address Block, in computer networking
Other uses International Accounting Bulletin, a UK accountancy publication