The renewed international interest in lunar exploration has made the establishment of reliable Positioning, Navigation and Timing (PNT) services beyond Earth orbit a strategic priority. As upcoming missions extend further into cislunar space and onto the lunar surface, autonomous navigation becomes essential to ensure operational continuity without constant reliance on ground-based tracking networks. Global Navigation Satellite Systems (GNSS), although originally designed for terrestrial and near-Earth users, have already demonstrated their usefulness for a variety of space applications. The Lunar GNSS Receiver Experiment (LuGRE), developed under an agreement between the Italian Space Agency (ASI) and NASA, has confirmed the feasibility of receiving and processing GPS and Galileo signals in cislunar space and on the lunar surface, demonstrating the potential of GNSS to support navigation well beyond Earth orbit.