CEI
- British Standard Whitworth
- Cei
- Central European Initiative
- Chiang Rai International Airport
- Chicago and Eastern Illinois Railroad
- Clean Energy Institute
- Cleveland Electric Illuminating Company
- College of Eastern Idaho
- Commission électorale indépendante (Democratic Republic of the Congo)
- Common Electrical I/O
- Comparably efficient interconnection
- Competitive Enterprise Institute
- Conferenza Episcopale Italiana
- Corporate Equality Index
- Council of Engineering Institutions
- Creative Engineering, Inc.