  We present a phenomenological approach to the description of single
transverse spin asymmetries (STSA) in inclusive hadron production. It
generalizes the pQCD formalism for high energies and large p_T inclusive hadron
production processes, A+B -> C+X, by incorporating quark intrinsic motion in
the spin dependent quark distribution and fragmentation functions. We
concentrate here on spin and k_T effects in the fragmentation process of a
polarized quark into the observed hadron, and give predictions for STSA in
semi-inclusive deep inelastic scattering, l + p -> pion + X and gamma^* + p ->
pion + X.
