  We summarize the renormalization-group properties of transverse-momentum
dependent (TMD) parton distribution functions (PDF)s arguing that in the
light-cone gauge the overlapping ultraviolet and rapidity divergences cannot be
solely controlled by (dimensional) regularization, but necessitate their
renormalization. In doing so, we show that at the one-loop order this
additional divergence entails an anomalous dimension which can be attributed to
a cusp in the gauge contour at light-cone infinity. Then, we present a recent
analysis of TMD PDFs which incorporates in the gauge links the Pauli term $\sim
F^{\mu\nu}[\gamma_\mu,\gamma_\nu]$. This generalized treatment of gauge
invariance is shown to be justified, in the sense that it does not modify the
behavior of the leading-twist contribution, though it contributes to the
anomalous dimension of that of twist-three. An important consequence of the
inclusion of the spin-dependent Pauli term is the appearance of a constant
phase---the same for the leading twist-two and subleading distribution
functions---that ensues from the interaction of the Pauli term in the
transverse gauge link with the gauge field accompanying the fermion.
Remarkably, this phase has opposite sign for the Drell-Yan process as compared
to the semi-inclusive DIS.
