Roughly half of all stars in the Universe are members of binary or other multiple-star systems. Interactions between the stars in these systems can lead to a wealth of stellar evolutionary outcomes, including black hole and neutron star binaries, and eventually be the source of gravitational waves resulting from black hole and neutron star merger events. Gaia—a space telescope that has built the largest and most precise three-dimensional map of our Galaxy—has provided unprecedented data for studying binary stars. A researcher at the California Institute of Technology (Caltech) has developed software to analyze Gaia data in order to characterize and catalog binary systems in the Galaxy, identify systems containing compact objects (i.e., black holes, neutron stars, white dwarfs), and study the physics of interacting stars. This project will support a graduate student, who will be involved with all aspects of the research, and it includes course development at Caltech and a workshop that will provide hands-on experience analyzing Gaia data for undergraduate and graduate students, as well as the broader astronomical community. The project also includes STEM training for K-12 teachers and high school students through a summer research program. Binary star systems play a critical role in understanding stellar evolution, particularly related to mass transfer and compact object formation. Gaia is transforming binary star science by detecting binary stars with separations that are largely inaccessible to other detection methods, thus opening up a whole new regime of binary systems. The principal investigator has produced an open-source software package (gaiamock) that models Gaia’s binary selection function and will use it to constrain the Galactic population demographics of post-interaction binaries, constrain the mass distribution of black holes and neutron stars, test models for the formation of compact-object binaries, constrain the role of binary envelope stripping i