Cosmic ray measurements around the knee

Primary cosmic rays of energy greater than ∼ 1014 eV must be studied by indirect experiments measuring the particles generated in the EAS (Extensive Air Shower) development in atmosphere. These experiments are mainly limited by the systematic errors due to their energy calibration. I will discuss the main sources of these errors: the choice of the hadronic interaction model and of the mass of the primary particle (that cannot be measured on a event by event basis). I will then summarize some recent measurements of the all particle spectrum, and I will show that, keeping into account the differences due to the energy calibration, they all agree on the spectral shape. Then I will describe the measurements of the light and heavy primaries mass groups spectra, discussing the claimed features. Using a simple calculation of the elemental spectra (based on the hypothesis that the knee energies follow a Peter's cycle) I will try to discuss if all these results can be interpreted in a common picture.