  Substellar multiplicity is a key outcome of the formation process. The
biggest challenge for the next decade will be to distinguish between the
formation history, environmental conditions, and dynamical evolution leading to
the least massive brown dwarfs and the most massive planets at the tail ends of
their mass functions. In this white paper, we advocate for a comprehensive
characterization of both the statistical distributions of the population of
ultracool dwarf multiple systems and the fundamental properties of their
individual components as a function of age. A space-based precision astrometry
mission in near-infrared wavelengths would provide the necessary measurements
to identify and characterize age-calibrated populations of multiple systems.
