The Lockman SpReSO survey is aimed at the optical spectroscopic study, using the near future MOS mode of OSIRIS at GTC, of sources up to magnitude 24.5 in the central 24x24 arcmin of the Lockman Hole field, which has been observed with XMM at the highest depth. Within the selected objects, optical counterparts of GALEX and Spitzer 24mu sources will be specifically targeted, together with special AGN samples and potential Submm galaxies. Some of the goals of this survey include studying the evolution of SFR and star formation efficiencies, optical vs. FIR extinctions, metallicities, stellar populations, stellar masses, and characterizing specific populations of high redshift objects such as AGNs, LAEs, SMGs and LIRGs-ULIRGs.