Low mass X-ray binaraies (LMXBs) are stellar binary systems consisting of a low-mass mass-losing star and a neutron star or, in some cases, a black hole. The neutron star or black hole accrete matter lost by the companion star. The accretion generally occurs via a disk and includes X-ray emission, flickering, and outbursts. The Principal Investigator proposes to study LMXBs in our galaxy and in the Large Magellanic Cloud and to determine mass transfer rates, the masses and radii of the component stars, and the range of diversity of these very interesting systems.