  I provide a conceptually-focused presentation of `low-energy quantum gravity'
(LEQG), the effective quantum field theory obtained from general relativity and
which provides a well-defined theory of quantum gravity at energies well below
the Planck scale. I emphasize the extent to which some such theory is required
by the abundant observational evidence in astrophysics and cosmology for
situations which require a simultaneous treatment of quantum-mechanical and
gravitational effects, \emph{contra} the often-heard claim that all observed
phenomena can be accounted for either by classical gravity or by
non-gravitational quantum mechanics, and I give a detailed account of the way
in which a treatment of the theory as fluctuations on a classical background
emerges as an approximation to the underlying theory rather than being put in
by hand. I discuss the search for a Planck-scale quantum-gravity theory from
the perspective of LEQG and give an introduction to the Cosmological Constant
problem as it arises within LEQG.
