  We present results from ultraviolet and X-ray observations of the low mass
X-ray binary Cygnus X-2. The simultaneous HST/GHRS and ASCA observations took
place during the low state of an 82-day cycle. We compare our observations as
well as archival IUE and RXTE data with models that predict ultraviolet and
optical continuum emission from an X-ray heated disk and a Roche-lobe-filling
star. The model predictions are consistent with observed optical, ultraviolet,
and X-ray variations over both orbital and long-term periods. The X-ray
spectral state, the luminosities implied by fits to the X-ray data, the
ultraviolet continuum and line fluxes, and the mass accretion rates obtained
from fits to the ultraviolet continuum are consistent with location of our
observations on the normal and horizontal branches of the Z-shaped X-ray
color-color diagram. A combination of changes to mass accretion rate and
obstruction by a warped disk can be invoked as a possible explanation for the
motion of the ``Z'' in the color-color plane. The GHRS/G160M measurements
concentrated on NV and HeII. The low-resolution (GHRS/G140L) observations
captured SiIV, NIV, and CIV. Although the relative line fluxes are consistent
with emission from an X-ray heated accretion disk corona, predictions from
models of line emission from simple disks do not fit the observed emission line
profiles.The radial velocities (80-130 km s$^{-1}$) are consistent with
emission from the optical star at the orbital phase (0.70-0.74) of our
observations.
