  We review the description of inclusive single unpolarized light hadron
production using fragmentation functions in the framework of the factorization
theorem. We summarize the factorization of quantities into perturbatively
calculable quantities and these universal fragmentation functions, and then
discuss some improvements beyond the standard fixed order approach. We discuss
the extraction of fragmentation functions for light charged and neutral hadrons
using these theoretical tools through global fits to experimental data from
reactions at various colliders, in particular from accurate e+e- reactions at
LEP, and the subsequent successful predictions of other experimental data, such
as data gathered at HERA, the Tevatron and RHIC from these fitted fragmentation
functions as allowed by factorization universality. These global fits also
impose competitive constraints on alpha_s(M_Z). Emphasis is placed on the need
for accurate data from ep and pp(pbar) reactions in which the hadron species is
identified in order to constrain the separate fragmentation functions of each
quark flavour and hadron species.
