- ZEI stands for ZEI, Inc. (not and acronym; formerly Zinder Engineering, Inc.)
- ZEI stands for Zenith Enterprises, Inc. (investment advisor; California)
- ZEI stands for Zentrum für Europaische Integrationsforschung (German: Center for European Integration Research; est. 1995)
- ZEI stands for Zone d’Epuration Individuelle (French: Area of Individual Purification; wastewater treatment; Belgium)
- ZEI stands for Zero Error Information
ZEI