Cosmic ray composition and energy spectrum above 1 TeV: direct and EAS   measurements
  The most recent experimental results on the cosmic ray composition and energy spectrum above 1 TeV are reviewed and discussed. All data agree on the presence of the so-called ``knee'' at an energy E(knee) = 3-4 PeV; the knee is seen in all the components of the Extensive Air Showers. These results support the hypothesis of an astrophysical origin of the knee, while no new features in the hadronic interactions at high energies are envisaged. The cosmic ray composition below and above the knee region is still an open question. According to most experiments, the knee seems to be due to the light component of the primary beam, with a composition getting heavier above the knee. However, results contradicting this conclusion have to be considered and understood. 
A.Castellina (Consiglio Nazionale delle Ricerche, Istituto di   Cosmogeofisica, cs.Fiume 4, Torino, Italy)