It is argued that, contrary to what is often said, large-transverse-momentum
hadronic processes studied at the ISR have made a significant contribution to
the understanding of the strong interaction and, in particular, to the
development of quantum chromodynamics. In their unique role as a gluon collider
the ISR have provided information that no other accelerator could have directly
offered. They allowed one to probe high values of the centre-of-mass energy
that were not available to fixed-target experiments. The latter, however, were
more flexible and, together, they allowed for powerful explorations of the
hadron structure and of the relevant dynamics in sectors such as inclusive
particle production, direct photon production, and jet structure studies. It
remains true that, rightly so, the ISR will be mostly remembered as the
founders of a lineage that includes the proton-antiproton colliders and, today,
the LHC.Comment: 12 pages, contribution to the CERN Yellow report: 40th Anniversary of
the First Proton-Proton Collisions in the CERN Intersecting Storage Rings
(ISR