  Extensive Air Showers are complex macroscopic objects initiated by single
ultra-high energy particles. They are the result of millions of high energy
reactions in the atmosphere and can be described as the superposition of
hadronic and electromagnetic cascades. The hadronic cascade is the air shower
backbone, and it is mainly made of pions. Decays of neutral pions initiate
electromagnetic cascades, while the decays of charged pions produce muons which
leave the hadronic core and travel many kilometers almost unaffected. Muons are
smoking guns of the hadronic cascade: the energy, transverse momentum, spatial
distribution and depth of production are key to reconstruct the history of the
air shower. In this work, we overview the phenomenology of muons on the air
shower and its relation to the hadronic cascade. We briefly review the
experimental efforts to analyze muons within air showers and discuss possible
paths to use this information.
