After the Big Bang, matter and antimatter were produced in equal quantities through materialization of the huge energy released. Observations show that today, however, there is a nearly total absence of antimatter in the Universe. The occurrence of Charge-Parity Violation (CPV) is a necessary condition for an explanation of this absence. CPV has already been observed in the quark sector but the measured amount is insufficient to explain the observed matter-antimatter asymmetry. Recent neutrino oscillation measurements indicate that the discovery of neutrino CPV becomes an important candidate to explain the observed matter dominance in the Universe. The goal of ESSnuSB project is to discover and measure neutrino CPV with unprecedented sensitivity. The ESSnuSB concept takes advantage of two outstanding opportunities. The first is the construction in Europe of the European Spallation Source, ESS, the world’s most intense proton source, with a beam power almost one order of magnitude higher than any other accelerator. The second is the recently measured unexpectedly large value of the oscillation mixing angle θ13. The latter fact implies that to obtain maximum sensitivity, the neutrino detector shall be placed at the second neutrino oscillation maximum, not at the first as implemented by the other proposed experiments. The Garpenberg mine in Sweden, in which it is proposed to install the underground neutrino detector, is situated at a distance from ESS that corresponds to the second maximum. The COST Action CA15139, “Combining forces for a novel European facility for neutrino-antineutrino symmetry-violation discovery”, already recognizes the necessity to have neutrino facilities in Europe. The goal of the ESSνSB H2020 Design Study is to organize European physicists and accelerator engineers in co-operation with the ESS Laboratory and the Garpenberg Mining Company to study and produce a Conceptual Design Report for the ESSnuSB project.