IIN and variants may mean:
International Institute for Nanotechnology at Northwestern University II-n or IIn, a subtype of Type II supernova Issuer Identification Number, a field in the ISO/IEC 7812 specification for ID cards IIN, ICAO airline code for Inter Islands Airlines IIN, IATA airport code for Nishinoomote Airport or Tanagashima Airport in the Ōsumi Islands Nieuport II.N, an airplane model iin, former stock ticker symbol for Australian ISP iiNet, now part of TPG Telecom