Fragmentation functions are non perturbative objects which are
needed to absorb consistently the singularities which appear in a
perturbative QCD calculation. These objects are only known by
comparing the experimental data and the theoretical predictions.
Moreover, these objects are also important in order to test the
factorization of the theory which impose also the universality of
them.
In this talk, we review the theoretical tools which are used for the
extraction of the parton-to-pion fragmentation functions. Then, we
show the results on the global NLO QCD fit to the data coming
from single inclusive electron-positron annihilation, semi-inclusive
deep-inelastic scattering and hadron-hadron collisions.