Abstract
Biological systems exhibit large-scale self-organized dynamics and structures
which enable organisms to perform the functions of life. The field of active
matter strives to develop and understand microscopically-driven nonequilibrium
materials, with emergent properties comparable to those of living systems. This
review will describe two recently developed classes of active matter systems,
in which simple building blocks --- self-propelled colloidal particles or
extensile rod-like particles --- self-organize to form macroscopic structures
with features not possible in equilibrium systems. We summarize the recent
experimental and theoretical progress on each of these systems, and we present
simple descriptions of the physics underlying their emergent behaviors.