  Transport measurements on two dimensional electron systems in moderate
magnetic fields suggest the existence of a spontaneously
orientationally-ordered, compressible liquid state. We develop and analyze a
microscopic theory of such a ``quantum Hall nematic'' (QHN) phase, predict the
existence of a novel, highly anisotropic $q^3$ density-director mode, find that
the T=0 long-range orientational order is unstable to weak disorder, and
compute the tunneling into such a strongly correlated state. This microscopic
approach is supported and complemented by a hydrodynamic model of the QHN,
which, in the dissipationless limit, reproduces the modes of the microscopic
model.
