HEP d.d. and HEP Group companies are collective members of many national and international organizations, institutions and associations:
- CIGRE (International Council on Large Electric Systems and CIGRE National Committee of Croatia
- ICOLD (International Commission of Large Dams)
- CIRED (Congres International des Réseaux Electriques de Distribution; and CIRED Croatian Branch)
- LWA (Live Working Association)
- EFET (European Federationof Energy Traders)
- IAEA (International Atomic Energy Agency)
- ENS (European Nuclear Society)
- UNICHAL (International Union of Heat Distributors)
- EUROHEAT & POWER (International organization focused on co-generations, long-distance heating and cooling)
- Croatian Academy of Engineering
- Croatian Energy Alliance
- Electrotechnical Society
- Croatian Nuclear Society
- Croatian Water Pollution Control Society
- Croatian Air Pollution Prevention Association
- Croatian Gas Association
- Croatian Business Council for Sustainable Development
- Croatia Green Building Council
- MIPRO Croatian Society
- Croatian Standards Institute
- Croatian Chamber of Economy
- German-Croatian Chamber of Industry and Trade
- Croatian-Austrian Chamber of Commerce
- CROMA – Croatian Managers' and Entrepreneurs' Association
