  For any fundamental quantum field theory, unitarity, renormalizability, and
relativistic invariance are considered to be essential properties. Unitarity is
inevitably connected to the probabilistic interpretation of the quantum theory,
while renormalizability guarantees its completeness. Relativistic invariance,
in turn, is a symmetry which derives from the structure of spacetime. So far,
the perturbative attempt to formulate a fundamental local quantum field theory
of gravity based on the metric field seems to be in conflict with at least one
of these properties. In quantum Ho\v{r}ava gravity, a quantum Lifshitz field
theory of gravity characterized by an anisotropic scaling between space and
time, unitarity and renormalizability can be retained while Lorentz invariance
is sacrificed at high energies and must emerge only as approximate symmetry at
low energies. I review various approaches to perturbative quantum gravity with
a particular focus on recent progress in the quantization of Ho\v{r}ava
gravity, supporting its theoretical status as a unitary, renormalizable and
ultraviolet-complete quantum theory of gravity.
