Despite tremendous progress in precision cosmology, several core mysteries remain, including the nature of dark energy, dark matter, and gravity. Galaxy surveys, which observe the positions and shapes of galaxies across large areas of the sky, are able to map a significant fraction of our cosmic volume, providing one of the most powerful probes of the Universe. I will describe how we use millions (or billions) of galaxies to measure both galaxy clustering and weak gravitational lensing, and how we learn about the Universe by analyzing these statistics. A significant challenge is that most of the Universe is “dark,” and we must infer from the roughly 5% visible fraction what the remaining 95% is doing. I will focus on the current state of the art, the Year 3 cosmology results from the Dark Energy Survey. I will also preview the exciting future of the field, with the Rubin Observatory and the Dark Energy Spectroscopic Instrument.
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