Modified gravitational wave propagation is a smoking gun of modifications of gravity at cosmological scales, and can be the most promising observable for testing such theories. The observation of gravitational waves (GW) in recent years has allowed us to start probing this effect, and here we briefly review two promising ways of testing it. We will show that, already with the current network of detectors, it is possible to reach an interesting accuracy in the estimation of the \Xi_0 parameter (that characterizes modified gravitational wave propagation, with \Xi_{0, {\rm GR}} = 1) and with next generation facilities, such as the Einstein Telescope, we can get a sub-percent measurement.
