  Underground muon events detected by the MACRO experiment at Gran Sasso have
been studied for different purposes. The studies include the vertical muon
intensity measurement, multiplicity distribution, lateral and angular muon
distribution and searches for substructures inside muon bundles. These analyses
have contributed to bring new insights in cosmic ray physics, in particular in
the framework of primary cosmic ray composition studies. Moreover, this
activity allows the testing and tuning of Monte Carlo simulations, in
particular for aspects associated with models of hadronic interactions and muon
propagation through the rock.
