  We present the perspective of using atom interferometry for gravitational
wave (GW) detection in the mHz to about 10 Hz frequency band. We focus on
light-pulse atom interferometers which have been subject to intense
developments in the last 25 years. We calculate the effect of the GW on the
atom interferometer and present in details the atomic gradiometer configuration
which has retained more attention recently. The principle of such a detector is
to use free falling atoms to measure the phase of a laser, which is modified by
the GW. We highlight the potential benefits of using atom interferometry
compared to optical interferometry as well as the challenges which remain for
the realization of an atom interferometry based GW detector. We present some of
the important noise sources which are expected in such detectors and strategies
to cirucumvent them. Experimental techniques related to cold atom
interferometers are briefly explained. We finally present the current progress
and projects in this rapidly evolving field.
