  Gamma-ray bursts (GRBs) display a bimodal duration distribution, with a
separation between the short- and long-duration bursts at about 2 sec. The
progenitors of long GRBs have been identified as massive stars based on their
association with Type Ic core-collapse supernovae, their exclusive location in
star-forming galaxies, and their strong correlation with bright ultraviolet
regions within their host galaxies. Short GRBs have long been suspected on
theoretical grounds to arise from compact object binary mergers (NS-NS or
NS-BH). The discovery of short GRB afterglows in 2005, provided the first
insight into their energy scale and environments, established a cosmological
origin, a mix of host galaxy types, and an absence of associated supernovae. In
this review I summarize nearly a decade of short GRB afterglow and host galaxy
observations, and use this information to shed light on the nature and
properties of their progenitors, the energy scale and collimation of the
relativistic outflow, and the properties of the circumburst environments. The
preponderance of the evidence points to compact object binary progenitors,
although some open questions remain. Based on this association, observations of
short GRBs and their afterglows can shed light on the on- and off-axis
electromagnetic counterparts of gravitational wave sources from the Advanced
LIGO/Virgo experiments.
