MOSAIC is the proposed visible and near-infrared multi-object spectrograph (MOS) for ESO’s forthcoming ELT.  The instrument is currently in the initial project stage known as Phase A. When operational MOSAIC will give the ELT the ability to obtain spectra for large samples of faint astronomical sources which are simply out of reach of ESO’s current facilities--from stars at the very heart of the Milky Way, out to the most distant galaxies at the edge of the observable Universe. I will discuss the top science cases for MOSAIC and identify the key technical requirements for each case. I will then present the instrument concept design and architecture that comply with these requirements, and will end by outlining the next steps for the project.