  Transverse-momentum spectra in hard processes are typically described either
in terms of intrinsic transverse momentum of partons, or in terms of
perturbative radiation. The relation between these descriptions is discussed
for the example of semi-inclusive deep inelastic scattering, with special focus
on the angular distribution of the observed hadron. This involves nontrivial
theoretical issues, such as the proper definition of transverse-momentum
dependent parton distributions, and has practical consequences for the
description of pT spectra in phenomenology.
