The hunt for dark matter has come to somewhat of a crossroads. Despite decades of intense effort on both experimental and theoretical fronts we are yet to find any direct evidence for new particles in experiment. Gravitational waves offer a number of unique and exciting opportunities to probe the dark sector including the `nightmare’ scenario where dark matter does not posses non-gravitational couplings to the Standard Model. Long baseline atom interferometers are set to open the window to mid-frequency (0.001-10 Hz) gravitational waves in the near future, broadening the range of new physics scenarios that we might hope to probe in this way. In this talk I will survey the landscape of possible contributions to the total ‘gravitational wave background’ within this frequency band, finding that the inspirals of known populations of stellar-mass compact binaries cumulatively produce a signal well within reach of proposed experiments. I will further show that hypothetical populations of dark sector exotic compact objects such as fermion and boson stars could generate signatures unique to mid- and low-frequency gravitational wave detectors, providing a novel means to probe complexity in the dark sector.