  We review the presence and signatures of the non-equilibrium processes, both
non-Maxwellian distributions and non-equilibrium ionization, in the solar
transition region, corona, solar wind, and flares. Basic properties of the
non-Maxwellian distributions are described together with their influence on the
heat flux as well as on the rates of individual collisional processes and the
resulting optically thin synthetic spectra. Constraints on the presence of
high-energy electrons from observations are reviewed, including positive
detection of non-Maxwellian distributions in the solar corona, transition
region, flares, and wind. Occurrence of non-equilibrium ionization is reviewed
as well, especially in connection to hydrodynamic and generalized
collisional-radiative modelling. Predicted spectroscopic signatures of
non-equilibrium ionization depending on the assumed plasma conditions are
summarized. Finally, we discuss the future remote-sensing instrumentation that
can be used for detection of these non-equilibrium phenomena in various
spectral ranges.
