  A VLA Sky Survey of the extragalactic sky at S band (2-4 GHz) with
polarization information can uniquely probe the magneto-ionic medium in a wide
range of astrophysical environments over cosmic time. For a shallow all-sky
survey, we expect to detect over 4 million sources in total intensity $>$ 0.45
mJy beam$^{-1}$ and over 2.2$\times$10$^5$ sources in polarized intensity. With
these new observations, we expect to discover new classes of polarized radio
sources in very turbulent astrophysical environments and those with extreme
values of Faraday depth. Moreover, by determining reliable Faraday depths and
by modeling depolarization effects, we can derive properties of the
magneto-ionic medium associated with AGNs, absorption line systems and
galaxies, addressing the following unresolved questions: (1) What is the
covering fraction, the degree of turbulence and the origin of absorption line
systems? (2) What is the thermal content in AGNs and radio galaxies? (3) How do
AGNs and galaxies evolve over cosmic time? (4) What causes the increase in
percentage polarization with decreasing flux densities at the low flux density
end of the polarized source count? (5) What is the growth rate of large-scale
magnetic fields in galaxies?
