The UA5 high energy pp simulation program

The UA5 Monte Carlo program, consisting of a non-diffractive event generator GENCL, a diffractive event generator DIFFR and a tracking program are described. The inputs to the event generators are explained in detail. Their outputs are compared to available data from the SppS Collider, and the agreement is shown to be good. The importance of some features of the generators are discussed. It is shown that cluster production and leading baryons are necessary to describe non-diffractive phenomena.