  We review the physical and cosmological consequences of two possible
electromagnetic couplings to the dark sector: (i) a neutral lightest
dark-matter particle (LDP) with nonzero electric and/or magnetic dipole moments
and (ii) a charged next-to-lightest dark-matter particle (NLDP) which decays to
a neutral LDP. For scenario (i) we find that a relatively light particle with
mass between a few MeV and a few GeV and an electric or magnetic dipole as
large as $\sim 3\times 10^{-16}e$ cm (roughly $1.6\times10^{-5} \mu_B$)
satisfies experimental and observational bounds. In scenario (ii), we show that
charged-particles decaying in the early Universe result in a suppression of the
small-scale matter power spectrum on scales that enter the horizon prior to
decay. This leads to either a cutoff in the matter power spectrum, or if the
charged fraction is less than unity, an effect in the power spectrum that might
resemble a running (scale-dependent) spectral index in small-scale data.
