  A range of issues pertaining to the use of Wilson lines in integrated and
transverse-momentum dependent (TMD) parton distribution functions (PDF) is
discussed. The relation between gauge invariance and the renormalization
properties of the Wilson-line integrals is given particular attention. Using an
anomalous-dimensions based analysis in the light-cone gauge, a generalized
definition of the TMD PDFs is proposed, which employs a cusped Wilson line, and
contains an intrinsic "Coulomb-like" phase.
