Jets and jet multiplicities in high-energy photon-nucleon interactions

We discuss the theory of jet events in high-energy photon-proton interactions using a model which gives a good description of the data available on total inelastic $\gamma p$ cross sections up to $\sqrt{s}=210\mathrm{}$ GeV. We show how to calculate the jet cross sections and jet multiplicities and give predictions for these quantities for energies appropriate for experiments at the DESY $\mathrm{ep}$ collider HERA and for very-high-energy cosmic ray observations.