  Active glassy matter has recently emerged as a novel class of non-equilibrium
soft matter, combining energy-driven, active particle movement with dense and
disordered glass-like behavior. Here we review the state-of-the-art in this
field from an experimental, numerical, and theoretical perspective. We consider
both non-living and living active glassy systems, and discuss how several
hallmarks of glassy dynamics (dynamical slowdown, fragility, dynamical
heterogeneity, violation of the Stokes-Einstein relation, and aging) are
manifested in such materials. We start by reviewing the recent experimental
evidence in this area of research, followed by an overview of the main
numerical simulation studies and physical theories of active glassy matter. We
conclude by outlining several open questions and possible directions for future
work.
