  In this paper we briefly review the transverse momentum dependent generalized
parton model and its application to the study of azimuthal asymmetries in the
distribution of leading hadrons (mainly pions) inside large transverse momentum
jets inclusively produced in polarized proton-proton collisions. We put
particular emphasis on the phenomenological interest of these observables, in
combination with similar asymmetries measured in semi-inclusive deeply
inelastic scattering, Drell-Yan processes and e+e- collisions, for the study of
the universality properties of the transverse momentum dependent parton
distribution and fragmentation functions. We present results for RHIC
kinematics at center-of-mass energies sqrt{s} = 200 and 500 GeV, for central
and mainly forward jet rapidities, in particular for the Sivers distribution
and the Collins fragmentation function, that are believed to be responsible of
many of the largest asymmetries measured in the last years. We also briefly
discuss the case of inclusive jet production and recent phenomenological
applications of other theoretical approaches, like the colour gauge invariant
generalized parton model and the collinear twist-three approach, aiming at
clarifying the issues of the universality and process dependence of transverse
momentum dependent functions.
