  We introduce the entangled coherent state representation, which provides a
powerful technique for efficiently and elegantly describing and analyzing
quantum optics sources and detectors while respecting the photon number
superselection rule that is satisfied by all known quantum optics experiments.
We apply the entangled coherent state representation to elucidate and resolve
the longstanding puzzles of the coherence of a laser output field, interference
between two number states, and dichotomous interpretations of quantum
teleportation of coherent states.
