  The orbital motion of the Laser Interferometer Space Antenna (LISA)
introduces modulations into the observed gravitational wave signal. These
modulations can be used to determine the location and orientation of a
gravitational wave source. The complete LISA response to an arbitary
gravitational wave is derived using a coordinate free approach in the
transverse-traceless gauge. The general response function reduces to that found
by Cutler (PRD 57, 7089 1998) for low frequency, monochromatic plane waves.
Estimates of the noise in the detector are found to be complicated by the time
variation of the interferometer arm lengths.
