  We present a QCD study of fragmentation processes for light and heavy quarks
in the semi-inclusive region of large x. Large logarithmic terms, due to
soft-gluon radiation, are evaluated and resummed to all perturbative orders in
the QCD coupling alpha_s. Complete analytical results to next-to-leading
logarithmic accuracy are given for one-particle and two-particle inclusive
distributions in e+e- annihilation and DIS. Factorization of parton radiation
at low transverse momenta is exploited to identify the universal
(process-independent) perturbative fragmentation function that controls
heavy-quark processes, and to perform next-to-leading logarithmic resummation
of its soft-gluon contributions. To gauge the quantitative impact of
resummation, we perform numerical studies of light- and heavy-quark
fragmentation in e+e- collisions.
