PYTHIA and JETSET are the two main components of the "Lund Monte Carlo" program suite. They can be used to generate high-energy-physics "events", i.e. sets of outgoing particles produced in the interactions between two incoming particles. Ideally these events should have the same average behaviour and the same fluctuations as real data. The underlying physics is not understood well enough to give an exact description; the programs therefore contain a combination of analytical results and various models. Several event classes are considered, within and beyond the standard model. We give a summary of the main physics component of the current versions, PYTHIA 5.7 and JETSET 7.4: hard scattering matrix elements, parton distributions, initial-and final-state radiation, multiple interactions, beam remnants, fragmentation and decays. A brief outline is also given of some programming aspects. A detailed physics description and manual is available as a separate publication.