  We briefly review the status of cosmic ray studies between $10^{14}$ eV and
the highest observed energies, namely a few times $10^{20}$ eV. Because of the
rather low incident fluxes in this energy range, the studies mostly rely on
ground based, large aperture detectors reconstructing the cosmic ray's
properties through the detection of the air-showers they generate by
interacting with the atmosphere. We stress the fact that many issues such as
the chemical composition of the cosmic rays, their acceleration mechanisms, the
structures displayed in their energy spectrum are mostly open questions which
may be answered by the next generation of experiments.
