  An assessment is offered of the progress that the major approaches to quantum
gravity have made towards the goal of constructing a complete and satisfactory
theory. The emphasis is on loop quantum gravity and string theory, although
other approaches are discussed, including dynamical triangulation models
(euclidean and lorentzian) regge calculus models, causal sets, twistor theory,
non-commutative geometry and models based on analogies to condensed matter
systems. We proceed by listing the questions the theories are expected to be
able to answer. We then compile two lists: the first details the actual results
so far achieved in each theory, while the second lists conjectures which remain
open. By comparing them we can evaluate how far each theory has progressed, and
what must still be done before each theory can be considered a satisfactory
quantum theory of gravity. We find there has been impressive recent progress on
several fronts. At the same time, important issues about loop quantum gravity
are so far unresolved, as are key conjectures of string theory. However, there
is a reasonable expectation that experimental tests of lorentz invariance at
Planck scales may in the near future make it possible to rule out one or more
candidate quantum theories of gravity.
