It is widely believed that the bulk of CRs up to about 10^17 eV is Galactic, produced and accelerated by the shock waves of SuperNova Remnants expanding shells. The main feature in the energy spectrum of Galactic Cosmic Ray is the so-called "knee", a steepening of the spectral index from -2.7 to -3.1 at about 3 PeV (=3x10^15 eV).
Understanding the origin of the "knee" is the key for a comprehensive theory of the origin of CRs up to the highest observed energies. In fact, the knee is connected with the issue of the end of the Galactic CR spectrum and the transition from Galactic to extra-galactic CRs.
We don't know if the "knee", is a source property, in which case we should see a corresponding spectral feature in the gamma-ray spectra of the CR sources, or the result of propagation, so we should observe a knee that is potentially dependent on location, because the propagation properties depend, in principle, on the position in the Galaxy.
An integrated and statistically significant measurement of the energy spectrum, elemental composition and anisotropy of the primary radiation in the "knee" energy region can be carried out only by ground-based EAS arrays.
In this talk the status of the measurements of Galactic Cosmic Rays in the "knee" energy domain will be summarized and the open problems introduced and discussed.
