  This paper reviews the theoretical and practical principles of the broadcast
approach to communication over state-dependent channels and networks in which
the transmitters have access to only the probabilistic description of the
time-varying states while remaining oblivious to their instantaneous
realizations. When the temporal variations are frequent enough, an effective
long-term strategy is adapting the transmission strategies to the system's
ergodic behavior. However, when the variations are infrequent, their temporal
average can deviate significantly from the channel's ergodic mode, rendering a
lack of instantaneous performance guarantees. To circumvent a lack of
short-term guarantees, the {\em broadcast approach} provides principles for
designing transmission schemes that benefit from both short- and long-term
performance guarantees. This paper provides an overview of how to apply the
broadcast approach to various channels and network models under various
operational constraints.
