AEI may refer to:
- Albert Einstein Institute, the Max Planck Institute for Gravitational Physics
- American Enterprise Institute
- Architectural Engineering Institute
- Archive of European Integration
- Associated Electrical Industries, large firm in the United Kingdom
- Automatic Equipment Identification, as used by the railroad industry
- AEI Music Network Inc., which merged with DMX (music) in 2001
- Alliance for European Integration, the ruling coalition in Moldova since the July 2009 election
- Aei (trigraph)