Gamma-ray burst emission: from low energy to high energy

Swift observations revealed interesting but puzzling afterglow behaviors that demand a rethinking of the origins of GRBs and their afterglows. In general, the observed X-ray afterglows include the contributions from both the external shock emission and late "internal" emission due to extended central engine activities. Recent observations and some theoretical efforts to interpret the data are highlighted. The high energy spectral regime will be fully revealed thanks to the launch and operation of several space and ground-based high energy detectors. Various physical processes that are predicted to contribute to high energy emission from GRBs are summarized, with comments on the most probable mechanisms of high energy emission in both the prompt and the afterglow phases.