🛡️ RISK BADGE: 🔴 HIGH (Strong Copyleft)
Executive Summary: What is it?
The European Union Public Licence (EUPL) is an OSI-approved strong copyleft licence published by the European Commission in all official EU languages with equal legal value. It is the reference licence for European public-sector software. Like the AGPL, its copyleft reaches network use: Article 1 defines "Distribution or Communication" to include providing access to the software's essential functionality online, so running a modified EUPL work as a service triggers the source-sharing obligation, unlike the plain GPL, which triggers only on distribution.
CFO / Business Impact: What does it cost/risk?
Moderate-to-high, with a built-in safety valve. Network and SaaS reach means modifications you deploy as a service must be released under the EUPL or a compatible licence. The distinctive feature is the compatibility clause: when EUPL code is combined with code under a listed licence (GPLv2/v3, AGPLv3, LGPL, MPL, EPL and others), the combined work may be distributed under that licence. This one-way upgrade path eases integration in a way the AGPL does not offer. The EUPL text itself cannot be unilaterally relicensed by recipients.
Technical Reality: How does it work?
Using EUPL software as-is, internally, triggers no obligations. Distributing it, or offering network access to a modified version, requires releasing your modifications under the EUPL or a compatible copyleft licence. For combined works, the target licence is chosen from the EUPL Appendix compatibility list. Treat it with the same diligence as the AGPL for any service you intend to modify and host.