  I review the distinguishing observational characteristics of active galaxies
with double-peaked emission lines and their implications for the nature of the
line-emitting region. Since double-peaked lines most likely originate in the
outer parts of the accretion disk, they can be used to study the structure and
dynamics of the disk and the associated wind. Such studies lead to general
inferences about the broad-line regions of all AGNs. To this end, I describe
the results of recent UV spectroscopy of double-peaked emitters that probes the
disk-wind relation. I also summarize efforts to exploit the variability of the
lines to study dynamical and thermal phenomena in the disk.
