IIN

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