  We address the role of fluctuations in strongly interacting matter during the
dense stages of a heavy-ion collision through its electromagnetic emission.
Fluctuations of isospin charge are considered in a thermal system at rest as
well as in a moving hadronic fluid at fixed proper time within a finite bin of
pseudo-rapidity. In the former case, we use general thermodynamic relations to
establish a connection between fluctuations and the space-like screening limit
of the retarded photon self-energy, which directly relates to the emissivities
of dileptons and photons. Effects of hadronic interactions are highlighted
through two illustrative calculations. In the latter case, we show that a
finite time scale $\tau$ inherent in the evolution of a heavy-ion collision
implies that equilibrium fluctuations involve both space-like and time-like
components of the photon self-energy in the system. Our study of non-thermal
effects, explored here through a stochastic treatment, shows that an early and
large fluctuation in isospin survives only if it is accompanied by a large
temperature fluctuation at freeze-out, an unlikely scenario in hadronic phases
with large heat capacity. We point out prospects for the future which include:
(1) A determination of the Debye mass of the system at the dilute freeze-out
stage of a heavy-ion collision, and (2) A delineation of the role of charge
fluctuations during the dense stages of the collision through a study of
electromagnetic emissivities.
