  I discuss the impact of the the coherent parton radiation on semi-inclusive
production of hadrons in deep inelastic scattering at lepton-proton colliders.
Such radiation can be consistently described in the $b$-space resummation
formalism, which was originally developed to improve theoretical description of
production of hadrons at $e^+e^-$ colliders and electroweak vector bosons at
hadron-hadron colliders. I present the detailed derivation of the resummed
cross section and the energy flow at the next-to-leading order of perturbative
QCD. The theoretical results are compared to the experimental data measured at
the $ep$ collider HERA. I argue that semi-inclusive deep inelastic scattering
(SIDIS) at lepton-hadron colliders offers exceptional opportunities to study
coherent parton radiation, which are not available yet at colliders of other
types.
