The unprecedented sensitivity provided by the ELT light-collecting area and its spatial resolution combined with a versatile multi-object spectrograph will enable the large samples of objects required by some of the fundamental scientific drivers of the ELT project. The MOSAIC multi-object spectrograph combines high-multiplex near-IR and visible spectroscopy, and AO-corrected spectroscopy in the near-IR in order to exploit the unprecedented angular resolution of the ELT across a very large field of view (32 arcmin2).

                MOSAIC will enable a comprehensive follow-up of very deep ground-based (e.g., LSST) and space-borne (Gaia, EUCLID) astrometric and imaging data, covering all the stellar populations in the Milky Way (including in particular the bulge, the Galactic center or the far side of the disk) and in galaxies out to the Fornax and Virgo clusters. MOSAIC will allow us to trace the distribution of matter (as well as dark matter and missing baryons) in the early Universe. We will understand how galaxies assemble by studying the oldest, most metal-poor stars and carrying out extensive surveys of the properties of high redshift galaxies.

                Scientific observations with MOSAIC will be obtained not only via the classical PI-proposals mode but also via large consortium and public surveys. In the context of phase B studies, and as the submission to ESO of the MOSAIC contract for construction is expected in June 2019, it is time to consolidate the efforts of the consortium, in particular to start designing the surveys in the light of the expected performances in order to best exploit the capabilities of MOSAIC.

                The last session of the meeting will include a round table with several scientific experts well recognized by the whole community.