  We present an overview on relational observables in gravity mainly from a
loop quantum gravity perspective. The gauge group of general relativity is the
diffeomorphism group of the underlying manifold. Consequently, general
relativity is a totally constrained theory with vanishing canonical
Hamiltonian. This fact, often referred to as the problem of time, provides the
main conceptual difficulty towards the construction of gauge-invariant local
observables. Nevertheless, within the framework of complete observables, that
encode relations between dynamical fields, progress has been made during the
last 20 years. Although analytic control over observables for full gravity is
still lacking, perturbative calculations have been performed and within
de-parameterizable toy models it was possible for the first time to construct a
full set of gauge invariant observables for a background independent field
theory. We review these developments and comment on their implications for
quantum gravity.
