The European Southern Observatory has approved the proposal for the MOSAIC instrument to pass into Phase A. MOSAIC is a multi-object spectro-graph to be mounted on the European Extremely Large Telescope, which will be the largest telescope on Earth for decades to come. MOSAIC has several scientific motivations ranging on all fields of contemporary astrophysics and cosmology, ranging from the earliest ‘first-light’ structures in the partially-reionised Universe to extra-solar planets. Claudia Maraston from the ICG is part of the MOSAIC scientific consortium and has contributed to the white paper by modelling the energy emission of primordial galaxies to define the optimal wavelength range and sensitivity for the instrument.