I will describe three major world-wide efforts to detect gravitational waves in three 
frequency bands. In the kilo-Hz band we use ground-based detectors (LIGO/Virgo), the 
milli-Hz band is accessible from space, I will describe LISA project, and, in the nano-Hz band we use millisecond pulsars (pulsar timing array). I'll briefly describe the GW sources and detection techniques in each band.