  This paper considers the problem of modeling the light polarization that
emerges from an astrophysical plasma composed of atoms whose excitation state
is significantly influenced by the anisotropy of the incident radiation field.
In particular, it highlights how radiative transfer simulations in
three-dimensional models of the quiet solar atmosphere may help us to probe its
thermal and magnetic structure, from the near equilibrium photosphere to the
highly non-equilibrium upper chromosphere. The paper finishes with predictions
concerning the amplitudes and magnetic sensitivities of the linear polarization
signals produced by scattering processes in two transition region lines, which
should encourage us to develop UV polarimeters for sounding rockets and space
telescopes with the aim of opening up a new diagnostic window in astrophysics.
