  We discuss the state-of-the-art of the theory of transverse-momentum
dependent parton densities (TMD)s, paying special attention to their
renormalization properties, the structure of the gauge links in the operator
definition, and the role of the soft factor in the factorization formula within
the TMD approach to the semi-inclusive processes. We argue that the use of the
lightcone axial gauge offers certain advantages for a consistent definition of
TMDs as compared to the off-the-light-cone gauges, or covariant gauges with
off-the-lightcone gauge links.
