Experiments at the CERN ISR have given evidence for proton single-dissociation processes where the missing mass of the system X, measured on the proton which is observed in the reaction p + p → p + X, presents a distribution extending up to large values , in the 10 GeV range. These processes globally account for ∼15% of the inelastic p-p cross section. Evidence for such a distinct class of inelastic phenomena is also provided by long-range rapidity correlations and clustering. The nature of these processes appears to be predominantly diffractive. The physics which emerges from ISR observations is discussed , together with a presentation of present and planned lines of experimental investigation at the ISR
