  Astrophysical plasmas have the remarkable ability to preserve magnetic
topology, which inevitably gives rise to the accumulation of magnetic energy
within stressed regions including current sheets. This stored energy is often
released explosively through the process of magnetic reconnection, which
produces a reconfiguration of the magnetic field, along with high-speed flows,
thermal heating, and nonthermal particle acceleration. Either collisional or
kinetic dissipation mechanisms are required to overcome the topological
constraints, both of which have been predicted by theory and validated with in
situ spacecraft observations or laboratory experiments. However, major
challenges remain in understanding magnetic reconnection in large systems, such
as the solar corona, where the collisionality is weak and the kinetic scales
are vanishingly small in comparison to macroscopic scales. The plasmoid
instability or formation of multiple plasmoids in long reconnecting current
sheets is one possible multiscale solution for bridging this vast range of
scales, and new laboratory experiments are poised to study these regimes. In
conjunction with these efforts, we anticipate that the coming era of exascale
computing, together with the next generation of observational capabilities,
will enable new progress on a range of challenging problems, including the
energy build-up and onset of reconnection, partially ionized regimes, the
influence of magnetic turbulence, and particle acceleration.
