The Dark Energy Survey (DES) is a galaxy survey which imaged one eight of the sky between 2013 and 2019, collecting data on the shapes and locations of more than 200 million galaxies. We use that data to study the large-scale distribution of matter in the Universe, and in turn to test our standard cosmological model to gain insight, for example, into the nature of the dark energy driving cosmic acceleration. This talk will introduce how we use the combined analysis of galaxy clustering and weak lensing to constrain cosmology, and will highlight recently released results constraining physics beyond the standard cosmological model using data from the first three years of DES observations. We will discuss studies of time-dependent dark energy equations of state, tests of general relativity as a description of gravity on cosmological scales, and limits on whether some fraction of dark matter is made up of a light but massive relic particle species.