Collaboration between European teams to build the astronomical Virtual Observatory has been funded by the European Commission though a series of projects which, between 2001 and 2014, were centred on collaborative work between European teams to develop the Virtual Observatory (VO) interoperability framework. The ASTERICS cluster was a new stage for the European Virtual Observatory: the VO was identified as one possible synergy within the cluster aim “to address cross-cutting synergies and common challenges shared by the Astronomy and Astroparticle ESFRI facilities”. That synergy was addressed by ASTERICS WP4, focused on Data Access, Discovery and Interoperability. The Work Package fully met its aims to build a collaboration between VO teams and the teams from the large ESFRI and ESFRI-like facilities, to support the community in the scientific usage of the VO, and to enable technological development of VO standards and tools customized to the facility needs. The facilities use the VO standards and tools for their own needs, and some of their staff have become actors in the development of the Virtual Observatory.