The highest-energy cosmic rays

This is a review of the experimental data concerning the spectrum, arrival distribution and composition of cosmic rays with energies greater than or equal to 10(19) eV. Before the experimental review I briefly discuss the conditions for the production followed by a review of the propagation of cosmic rays. Then follows a discussion of the properties of the showers produced by the primary cosmic ray particles and a description of the techniques used to detect the showers and extract the energy, direction and nature of the primary. The main conclusion of the experimental review is that there is still insufficient data to answer all the questions concerning the particles which strike the earth with such enormous energies. There has been significant progress which I will discuss and there are good prospects that in the next five years we will come much closer to the answers. Much more can be learned from existing data but a more sophisticated and disciplined analysis will be required.