The European Spallation Source (ESS) presently in construction in Lund (Sweden) will deliver neutron beams of unprecedented brightness to a new generation of scientific instruments. Generated by the 5 MW proton beam from a 2 GeV superconducting linac impacting a rotating tungsten target, the spallation neutrons will be slowed down in a set of moderators/reflectors. A total of 42 guides will be available to conduct them out of the target monolith to the different instruments. ESS being a “green-field” facility, it is still recruiting and maturing while construction proceeds. Major laboratories and institutions all across Europe are partnering with the ESS teams to help address the technical challenges inherent to the construction of such a state-of-the-art facility. Once in nominal operation in 2025 with between 16 and 22 instruments running, beam lines will remain available for installing up to a dozen more. Synergy with the world-class synchrotron light facility MAX-IV located on the same site will be especially attractive. In the longer term, the unique characteristics of ESS will also give rise to proposals for experiments on other physics subjects, possibly exploiting the upgrade potential of the facility. Challenges are described in this paper, as well as the way they are addressed. Medium- and long-term perspectives are sketched.