The study of cosmic rays at primary energies E o > 10 14 eV requires the detection of the different components of Extensive Air Showers through ground based stations. EAS-TOP is such an array (located at Campo Imperatore 2000 m a.s.l., National Gran Sasso Laboratories), including detectors of the electromagnetic, muon (Eμ, ≈ GeV at the surface, and Eμ, ≈ TeV in coincidence with the detectors operating in the underground Gran Sasso Laboratories), hadron and atmospheric Cerenkov light components. The combined operation of the detectors is discussed from the point of view of the capability of measuring the cosmic ray primary spectrum and composition. The main lines for checking the significant features of the high energy hadron interaction model used for the interpretation of the data are outlined.