  Microlensing is a proven extrasolar planet search method that has already
yielded the detection of four exoplanets. These detections have changed our
understanding of planet formation ``beyond the snowline'' by demonstrating that
Neptune-mass planets with separations of several AU are common. Microlensing is
sensitive to planets that are generally inaccessible to other methods, in
particular cool planets at or beyond the snowline, very low-mass (i.e.
terrestrial) planets, planets orbiting low-mass stars, free-floating planets,
and even planets in external galaxies. Such planets can provide critical
constraints on models of planet formation, and therefore the next generation of
extrasolar planet searches should include an aggressive and well-funded
microlensing component. When combined with the results from other complementary
surveys, next generation microlensing surveys can yield an accurate and
complete census of the frequency and properties of planets, and in particular
low-mass terrestrial planets.
