EUPL is an acronym for "European Union Public Licence".
The first EUPL draft (v.0.1) went public in June 2005. A public debate was then organised by the European Commission (IDABC). The consultation of the developers and users community was very productive and has lead to many improvements of the draft licence; 10 out of 15 articles were modified. Based on the results of these modifications (a detailed report and the draft EUPL v.0.2), the European Commission elaborated a final version (v.1.0) that was officially approved on 9 January 2007, in three linguistic versions.
By a second Decision of 9 January 2008, the European Commission validated the EUPL in all the official languages of the European Union.
By a third Decision of 9 January 2009, the European Commission clarified specific points of the EUPL, publishing the version 1.1 in all the official languages of the European Union.
The Commission Implementing Decision (EU) 2017/863 of 18 May 2017 updating the open source software licence EUPL to further facilitate the sharing and reuse of software developed by public administrations (OJ 19/05/2017 L128 p. 59–64 ) published the version 1.2, with extended compatibility.
The purpose of the European Commission is first of all to distribute its own software under the licence. Some applications developed in the framework of the IDABC programme, such as Circabc, or Eusurvey have already been licensed under the EUPL in 2007. Other European Institutions are also interested in using the new licence.
But why creating a new legal instrument from scratch when more than 100 other F/OSS licences exist, such as the GPL, the BSD or the OSL? The reason is that in a detailed legal study no existing licence was found to correspond to the requirements of the European Commission:
The main objective of the European Commission is to distribute widely and promote the use of software owned by itself and other European Institutions under an Free/Open Source Licence conform to European law requirements.
The EUPL is however written in neutral terms so that a broader use might be envisaged.
In addition, distribution of software should avoid the exclusive appropriation of the software even after improvement by a third party (therefore, the EUPL is a "copyleft" licence).
Although the potential users of European Institutions' software are mostly other public sector administrations, there is nothing in the EUPL preventing its broader use. The EUPL could be used by anyone who holds the copyright to a piece of software. It could become – in various languages - an adequate legal interoperability instrument across Europe.
Nevertheless, the EUPL purpose is not to compete with other licences. It might be used primarily by public administrations, either European or national, that would need a common licensing instrument to mutualise or share software and knowledge.
Yes, it is. The EUPL contains a unique compatibility clause and provides for a list of compatible copyleft licences. The GPL is one of them.
For example, how would the interaction between the EUPL and the GPL play out in the case of CIRCA, an application a already distributed under the EUPL?
A developer may merge the Circabc software with a GPL component, and then could license the new derivative work (another project, with a new name) under the GPL. It is not permitted to "re-license" CIRCA under the GPL. A developer will be also able to integrate CIRCA in existing GPL work called e.g. "MY-GPL-PROGRAM" and continue to license this improved work under the GPL licence that he had chosen originally.