DEI is a three-letter acronym. It may refer to one of the following:
- DEI (Greek national electrical company)
- FIFA Trigramme for Dutch East Indies
- Dale Earnhardt, Inc., a current NASCAR team
- DEI, Dayalbagh Educational Institute, university in Agra, India
- DEI (Dabney Eats It), the lounge in Dabney House at Caltech. Also serves as Dabney House's motto.
- Data Expedition, Inc., an enterprise software company that produces software for the data transfer market.
- Destroy Erase Improve, a 1995 album by Swedish heavy metal band Meshuggah
- Directed Electronics, Inc., manufacturer of vehicular audio and security systems, including the popular Clifford and Viper car alarm systems.
- Dutch East Indies, Indonesia when it was still a Dutch Colony
- Dawat-e-Islami : A non-political Islam preaching organization