  Relic neutrinos play an important role in the evolution of the Universe,
modifying some of the cosmological observables. We summarize the main aspects
of cosmological neutrinos and describe how the precision of present
cosmological data can be used to learn about neutrino properties. In
particular, we discuss how cosmology provides information on the absolute scale
of neutrino masses, complementary to beta decay and neutrinoless double-beta
decay experiments. We explain why the combination of Planck temperature data
with measurements of the baryon acoustic oscillation angular scale provides a
strong bound on the sum of neutrino masses, 0.23 eV at the 95% confidence
level, while the lensing potential spectrum and the cluster mass function
measured by Planck are compatible with larger values. We also review the
constraints from current data on other neutrino properties. Finally, we
describe the very good perspectives from future cosmological measurements,
which are expected to be sensitive to neutrino masses close the minimum values
guaranteed by flavour oscillations.
