  From the late 1920s to the early 1950s, cosmic rays were the main instrument
to investigate what we now call "high-energy physics". In approximately 25
years, an intense experimental and theoretical work brought particle physics
from its childhood to its maturity. The data collected at that time played a
crucial role in order to outline the quantum theories of fundamental
interactions - electromagnetic, weak and strong - and they were an excellent
training field for many young scientists. The knowledge acquired on cosmic rays
constituted the basis of the extraordinary progresses that were to be achieved
in fundamental physics with the introduction of particles accelerators.
  Many papers on this subject have already been published, both by historians
and by the scientists who personally worked at that time. However, a complete
historical reconstruction of those 25 years of cosmic-ray researches has not
been written yet. In particular, an overall description of the researches
carried out with the contributions of Italian physicists is still missing. The
present paper tries to outline such a description, taking into account the fact
that in those very years, for scientific and non scientific reasons, physics
researches were getting organised within international collaborations. Without
pretending to be exhaustive at all, we would like this paper to be a stimulus
for further researches on the subject.
