The unknown nature of dark matter already represents one of the greatest gaps in our understanding of the universe. But the study of dark matter is now encountering a crisis: collider searches and direct detection experiments are quickly ruling out the strongly-motivated WIMP models that have guided theoretical progress for decades. Departing from the WIMP paradigm opens vast regions of parameter space across the scales, from ultralight bosons to objects at the Planck scale and beyond, and effectively probing this space of possibilities calls for new tools. Fortuitously, several such tools are available to us in the form of new quantum sensors, new astrophysical observables, and the new science of gravitational wave astronomy. In this thesis, I show how these methods can be combined to probe well-motivated dark matter candidates across an enormous range of masses.