  The premise of "near-field cosmology" is that the study of nearby low-mass
galaxies on a star-by-star basis has implications that extend far beyond the
local Universe and include the nature of dark matter, lives and deaths of the
first stars, cosmic reionization, and galaxy formation across cosmic time. In
response to the Astro2020 call for science white papers, we provide a
high-level synopsis of several major questions in near-field cosmology, the
potential for transformative progress in the next decade and beyond, and
mechanisms for achieving these goals. Our recommendations include: (i)
obtaining kinematic information from large samples of individual line-of-sight
and transverse velocities of stars and from spatially resolved gas observations
in nearby dwarf galaxies to directly inform our understanding of dark matter
interactions in the deeply nonlinear regime; and (ii) an intensive program of
optical imaging and UV and optical spectroscopy of resolved stars in low-mass
galaxies, including low-metallicity massive stars and HII regions (which are
central to understanding faint galaxies at all earlier epochs). Realizing these
aims requires a large aperture ($\gtrsim 9$m) UV/optical space telescope, a
two-fold community investment in ground-based optical spectroscopy through both
ELTs and a dedicated wide-field spectroscopic survey on a 10m class telescope,
and radio facilities that can measure high-precision, spatially resolved
rotation curves of low-mass galaxies. Finally, we suggest that a servicing
mission to extend the life of HST beyond 2025 should be seriously explored.
