  A generic synchrotron external shock model is the widely preferred paradigm
used to interpret the broad-band afterglow data of gamma-ray bursts (GRBs),
including predicted observable signatures from a reverse shock which have been
confirmed by observations. Investigations of the nature of the reverse shock
emission can provide valuable insights into the intrinsic properties of the GRB
ejecta. Here we briefly review the standard and the extended models of the
reverse shock emission, discussing the connection between the theory and
observations, including the implications of the latest observational advances.
