  The propagation of colored quarks through strongly interacting systems, and
their subsequent evolution into color-singlet hadrons, are phenomena that
showcase unique facets of Quantum Chromodynamics (QCD). Medium-stimulated gluon
bremsstrahlung, a fundamental QCD process, induces broadening of the transverse
momentum of the parton, and creates partonic energy loss manifesting itself in
experimental observables that are accessible in high energy interactions in hot
and cold systems. The formation of hadrons, which is the dynamical enforcement
of the QCD confinement principle, is very poorly understood on the basis of
fundamental theory, although detailed models such as the Lund string model or
cluster hadronization models can generally be tuned to capture the main
features of hadronic final states. With the advent of the technical capability
to study hadronic final states from lepton scattering with good particle
identification and at high luminosity, a new opportunity has appeared. Study of
the characteristics of parton propagation and hadron formation as they unfold
within atomic nuclei are now being used to understand the coherence and spatial
features of these processes and to refine new experimental tools that will be
used in future experiments. Fixed-target data on nuclei with lepton and hadron
beams, and collider experiments involving nuclei, all make essential contact
with these topics and they elucidate different aspects of these same themes. In
this paper, a survey of the most relevant recent data and its potential
interpretation will be followed by descriptions of planned experiments at
Jefferson Lab following the completion of the 12 GeV upgrade, and feasible
measurements at a future Electron-Ion Collider.
