  The search for a quantum theory of gravity has been one of the main aims of
theoretical physics for many years by now. However the efforts in this
direction have been often hampered by the lack of experimental/observational
tests able to select among, or at least constrain, the numerous quantum gravity
models proposed so far. This situation has changed in the last decade thanks to
the realization that some QG inspired violations of Lorentz symmetry could be
constrained using current experiments and observations. This study it is not
only allowing us to test at higher and higher energies a fundamental symmetry
of spacetime but it is also providing us with hints and perspectives about the
fundamental nature of gravity.
