  The description of the internal structure of hadrons is one of the main goal
of QCD. At moderate energy scales, the hadronic representation succeeds to the
partonic description, rendering challenging the description of the dynamics of
scattering processes and hadronic structure. The information on the hadron
structure is embodied in the long distance contributions which are defined as
Parton Distribution Functions (PDFs). PDFs are a key framework for connecting
the low and high-energy regimes, in that the knowledge on non- perturbative QCD
carries important consequences at the high-energy level. We here review recent
progress in the description of the proton, from complementary approaches such
as fits of PDFs, phenomenological analyses and experimental predictions in view
of the JeffersonLab upgrade and applications for high-energy colliders.
