Inelastic proton-air cross section in U.H.E

We calculate the inelastic proton-air cross section by means of the Glauber model. As input, we use accelerator experimental data on the total proton-proton cross section and compare with cosmic ray experimental data and Monte Carlo simulations. Contribution to the 26th International Cosmic Ray Conference, Salt Lake City, Utah. HE 1.3.13. August, 1999.