  Gamma-ray bursts (GRBs) are short and intense emission of soft gamma-rays,
which have fascinated astronomers and astrophysicists since their unexpected
discovery in 1960s. The X-ray/optical/radio afterglow observations confirm the
cosmological origin of GRBs, support the fireball model, and imply a
long-activity of the central engine. The high energy gamma-ray emission (>20
MeV) from GRBs is particularly important because they shed some lights on the
radiation mechanisms and can help us to constrain the physical processes giving
rise to the early afterglows. In this work, we review observational and
theoretical studies of the high energy emission from GRBs. Special attention is
given to the expected high energy emission signatures accompanying the
canonical early-time X-ray afterglow that was observed by the Swift X-ray
Telescope. We also discuss the detection prospect of the upcoming GLAST
satellite and the current ground-based Cerenkov detectors.
