EAS Longitudinal Development and the Knee

It is shown that Extensive Air Shower (EAS) longitudinal development has a critical point where an equilibrium between the main hadronic component and the secondary electromagnetic one exhibits a brake. This results in a change of slope in quasi-power law function $N_e(Eo)$. The latter leads to a knee in the EAS size spectrum at primary energy of about 100 TeV/nucleon. Many ``strange’’ experimental results can be successfully explained in the frames of current approach.