Within this decade the detection of gravitational waves (GWs) may be a reality, opening a completely new window on the Universe. At nHz frequencies, pulsar timing arrays (PTAs) promise to detect the signal coming from the cosmological population of supermassive black hole binaries SMBHBs within the next few years. After rewiewing the astrophysics of SMBHBs, I will describe the current status of the PTA effort, and cast prospects of detection and astrophysical payouts.