IEI may mean: Idiopathic environmental intolerance, also known as multiple chemical sensitivity. Inborn errors of immunity, genetic mutations that cause an increased susceptibility to disease. Intensive English Institute, at the University of Illinois Urbana-Champaign. Institut d'échanges interculturels. Institute for Emerging Issues. Institution of Engineers (India) Institution of Engineers of Ireland. Intuitive Ethical Introvert, in socionics theory. Iran Electronics Industries
https://en.wikipedia.org/wiki/IEI