  An array of powerful neutrino-beam experiments will study the fundamental
properties of neutrinos with unprecedented precision in the coming years. Along
with their primary neutrino-physics motivations, there has been growing
recognition that these experiments can carry out a rich program of searches for
new, light, weakly-coupled particles that are part of a dark sector. In this
white paper, we review the diverse theoretical motivations for dark sectors and
the capabilities of neutrino beam experiments to probe a wide range of models
and signatures. We also examine the potential obstacles that could limit these
prospects and identify concrete steps needed to realize an impactful dark
sector search program in this and coming decades.

High Energy Physics - Phenomenology;High Energy Physics - Experiment