Microlensing and Halo Cold Dark Matter

We discuss the implications of the more than 50 microlensing events seen by the EROS, MACHO, and OGLE collaborations for the composition of the halo of our galaxy. The event rates indicate that the halo mass fraction in MACHO’s is less than 30%, consistent with expectations for a universe whose primary component is cold dark matter. We caution that the uncertainties are such that a larger MACHO fraction cannot yet be excluded.