Gamma-ray bursts (GRBs) have long been among the most enigmatic of
astrophysical transients. Observations during the past decade have
led to a revolution in our understanding of long-duration GRBs,
associating these events with the core-collapse of massive stars.
However, only in the past few years have the host galaxies of
short-duration GRBs been established, confirming that these arise from
a separate progenitor population; the leading model for such events is
the merger of two compact objects (e.g., a neutron star and a black
hole) although alternative possibilities remain viable (e.g., the
accretion induced collapse of a white dwarf to a neutron star). In
this talk, I will describe theoretical models for both long and
short-duration bursts, emphasizing several outstanding problems.
Short GRBs are particularly interesting since compact object mergers
are the primary target for km-scale gravitational wave observatories
such as Advanced LIGO. I will describe possible electromagnetic
counterparts to these gravitational wave sources.