  Within this decade gravitational wave detection will open a new observational
window on the Universe. Advanced ground based interferometers covering the kHz
frequency range will be online by 2016, and it is foreseeable the announcement
of a first detection within five years. At the same time, a worldwide effort of
detecting low frequency waves (in the nHz regime) by timing ultra-precise
millisecond pulsars is rapidly growing, possibly leading to a positive
detection within this decade. The mHz regime, bridging these two windows, is
the realm of space based interferometers, which might be launched in the late
20s. I provide here a short overview of the scientific payouts of gravitational
wave astronomy, focusing the discussion on the low frequency regime (pulsar
timing and space based interferometry). A detailed discussion of advanced
ground based interferometer can be found in Patrick Brady's contribution to
this proceedings series.
