There is the possibility that GPL's viral nature is not actually fully possible in EU and EUPL is "the most" you can get copyleft-wise there. There are two arti

There is the possibility that GPL's viral nature is not actually fully possible in EU and EUPL is "the most" you can get copyleft-wise there. There are two articles about it on the EC's site: https://joinup.ec.europa.eu/collection/eupl/news/why-viral-licensing-ghost https://joinup.ec.europa.eu/collection/eupl/news/why-viral-l... === (relevant snippet) As a conclusion, it looks that in most cases, linking two programs or linking an existing software with your own work does not – at least in Europe – produce a derivative or extends the coverage of the linked software licence to your own work. Such interfacing or linking escapes to the copyleft provision of any licence, open source (like the GPL) or proprietary. The technical way of linking for interoperability (static or dynamic, permanent or temporary reproduction of the needed code) should not make any difference. Because of this, and in so far linking (even statically) is done for interoperability, does not prejudices the legitimate interests of the rightholder and does not conflict with a normal exploitation of the covered program, it seems that the differentiation between strong and weak copyleft has few legal reality. In applying all relevant licences, the copyleft effect should target the copies and real derivative works, where a significant portion of the functional covered code has been copied, modified, extended etc. At the contrary and in most cases, it seems that in European law the fact of linking two programs and the technology used for it does not by itself produce a derivative work: viral licensing is just a ghost. It does not exist. === This article (from the same author) also goes into virality in EU: https://joinup.ec.europa.eu/collection/eupl/news/copyleft-or-reciprocal https://joinup.ec.europa.eu/collection/eupl/news/copyleft-or... === (relevant snippets) Although often highlighted by some free software lawyers, this notion of “strong copyleft” has never been recognized by case law. On 2 May 2012, the Court of Justice of the European Union ruled that a software licence cannot prohibit the legitimate licensee from reproducing the portions of covered code (for example, the APIs or data structures) that are necessary for interoperability and for linking the covered work with others that could be licensed differently. This was ruled in application of the Directive 91/250 EEC on the legal protection of computer programs. [...] At the contrary and in all cases, it seems that in European law the fact of linking two programs and the technology used for it (i.e. dynamic or static) does not by itself produce a derivative work. This is the reason why it was considered that adding copyleft licences like the LGPL or the MPL to the EUPL compatibility list was not more problematic than adding the GPLv3 or the AGPL. === It should be noted, however, that this hasn't been explicitly tested in court with open source software (the software case mentioned in the second article was between proprietary software developers). Also in practice most projects aren't released in just the EU so the GPL's strong copyleft still holds true in US, for example, even for work done in the EU. But this isn't a concern for the European Commission since the EUPL was made for EU use.