The seemingly un-magnetized part of the solar surface is not really un-magnetized. It is occupied by magnetic structures producing low polarization which, therefore, escape detection in traditional measurements. Since most of the solar surface belongs to this category, the quiet Sun magnetic fields can easily carry most of the magnetic flux and energy existing in the photosphere at any given time. Consequently, they are a potentially important ingredient of the solar magnetism. Most of the physical properties of the quiet Sun are still uncertain (distribution of field strengths, area coverage, influence on higher atmospheric layers, etc.).It is clear, however, that the topology of the field is complex, with field lines of very different properties coexisting in each resolution element. This fact hampers the detection of the quiet Sun magnetic fields. I argue that the best present measurements detect, at most, 30 % of the existing magnetic flux. Then the quiet Sun contains at least as much magnetic flux as all active regions and the network during the solar maximum.