  The role of intrinsic transverse momentum both in unpolarized and polarized
processes is discussed. We consider inclusive cross sections for pion
production in hadronic collisions and for Drell-Yan processes; the results are
compared with available experimental data in several different kinematical
situations. We reanalyze transverse single spin asymmetries (SSA) observed in
inclusive pion production, p(transv. polarized) p --> pion + X, in terms of
Sivers effect and show how it can be disentangled in polarized Drell-Yan
processes by suitably integrating over some final configurations. Estimates for
RHIC experiments are given.
