One specific point was raised during the recent June 12th EC workshop “OPEN STANDARDS FOR ICT PROCUREMENT: SAVING WHILE REDUCING ICT LOCK-IN”: How far could software licensed under the EUPL be used in a commercial or in a proprietary application?
The European Union Public Licence (EUPL) is a copyleft open source licence, in order to protect the covered work from exclusive appropriation. “Copyleft” means that if a software “Code A” is covered by the EUPL, this is forever: nobody may re-licence “A” and its modifications (or derivatives) under a different licence.
However important remarks need to be formulated:
This makes no obstacle to commercial use. Anyone can sell software or services using or including “Code A” or use it for a commercial activity. Open source and non-commercial are not synonyms.
This makes no obstacle for linking Code A with another software component (Code B) that could be proprietary. There is no kind of “viral effect” resulting from the EUPL licence, in so far linking is done for interoperability. The portions of Code A that are strictly necessary for interoperability may be reproduced in Code B without copyright infringement. The resulting “A-B solution”, which could be commercial, will include the two modules under their relevant licences. This is resulting from interpreting European law and case law.
The EUPL v1.1 provides exceptions to the obligation to license derivatives of Code A under the EUPL: when needed, “Code A” or substantial portions of it, more than what is needed for interoperability, may be merged in another derivative project “Code B”, licensed under a compatible licence: GPL v2 (and v3 implicitely), OSL, EPL or CeCILL.
- The EUPL v1.2 (text is final, waiting official publication) covers “the work” more generally, including non-software works: data, standards, specifications, and it extends the list of compatible licences to GPL v3 (explicitely), AGPL v3, LGPL, MPL, CC BY SA (for works other than software).
Here also, the code or work B could be part of a commercial use or solution, provide the licensing conditions are respected, as the publication of the source code in so far the relevant applicable licence is open source.
It is important to consider all the above remarks, because some other sources or non-EU web sites have published comments on the EUPL or on linking in general, which look wrong or without legal basis.
For more details and legal considerations, please refer to the EUPL analysis in the December 2013 issue of the International Free and Open Source Software Law Review (IFOSSLR).
 Interpretation of Directive 2009/24/EC on the legal protection of computer programs (art 6, 1. a & b) and Court of Justice of the EU – Case C-406/10 of 2 May 2012.
 “when needed” means when other substantial portions of Code B were obtained under another copyleft licence (e.g. GPL) making the reuse of this copyleft licence mandatory for distributing Code B. The compatibility of EUPL v1.1 with the Gnu GPLv3 is implicit/indirect (e.g. resulting with compatibility with CeCILL).