On September 14, 2015, the direct observation of a system of coalescing black holes thorough their gravitational waves emission marked the beginning of a new era for astronomy. Just two years later, observation of the gravitational wave signal by a pair of coalescing neutron stars enabled an unprecedented observational campaign of the same system throughout the whole electromagnetic spectrum. We now have a powerful, new complementary channel to observe our universe, enabling us to greatly enrich our picture of the Cosmo. I will briefly introduce gravitational waves, their observed and expected sources and the observatories we use (and will use) to detect them. I will conclude by reviewing the observations performed so far.