IIA

IIA or Iia may refer to:
 * Independence of irrelevant alternatives
 * Indian Institute of Architects
 * Indian Institute of Astrophysics
 * Indianapolis International Airport
 * Institute of Internal Auditors
 * Information Industry Association
 * International Investment Agreement
 * Islamabad International Airport
 * IIa or II-a, a subtype of Type II supernova
 * A rating in the Hong Kong motion picture rating system
 * Iia, Estonia, village in Estonia