Abstract: Over the six years of 2013-2019, the Dark Energy Survey (DES) imaged one eighth of the sky, measuring the properties of hundreds of millions of galaxies. In this talk I will discuss how we leverage these data to probe the geometry and growth of structure in our Universe, and through that, to test models describing the physics of dark energy, dark matter, and gravity. I will present results from the DES Year 6 cosmology analysis of galaxy clustering and weak gravitational lensing, and will highlight how, as the largest-area galaxy imaging survey of its kind, DES serves as a laboratory for preparation for analysis with next-generation cosmological experiments like the Vera Rubin Observatory Legacy Survey of Space and Time (LSST).