  We analyze the transverse momentum dependent distribution and fragmentation
functions in space-like and time-like hard processes involving at least two
hadrons, in particular 1-particle inclusive leptoproduction, the Drell-Yan
process and two-particle inclusive hadron production in electron-positron
annihilation. As is well-known, transverse momentum dependence allows for the
appearance of unsuppressed single spin azimuthal asymmetries, such as Sivers
and Collins asymmetries. Recently, Belitsky, Ji and Yuan obtained fully color
gauge invariant expressions for the relevant matrix elements appearing in these
asymmetries at leading order in an expansion in the inverse hard scale. We
rederive these results and extend them to observables at the next order in this
expansion. We observe that at leading order one retains a probability
interpretation, contrary to a claim in the literature and show the direct
relation between the Sivers effect in single spin asymmetries and the
Qiu-Sterman mechanism. We also study fragmentation functions, where the process
dependent gauge link structure of the correlators is not the only source of
T-odd observables and discuss the implications for universality.
