  Quantum gravity is sometimes considered as a kind of metaphysical
speculation. In this review, we show that, although still extremely difficult
to reach, observational signatures can in fact be expected. The early universe
is an invaluable laboratory to probe "Planck scale physics". Focusing on Loop
Quantum Gravity as one of the best candidate for a non-perturbative and
background-independant quantization of gravity, we detail some expected
features.
