Abstract: Small-scale cosmic structure offers a rapidly developing window into dark matter and the primordial universe. I will first present prompt cusps -- compact dark matter systems that form at the onset of structure formation and persist at halo centers. Their tight connection to the initial conditions makes them a precision tool for cosmology on small scales. Applications include new warm dark matter limits from ultrafaint dwarf kinematics, an order-of-magnitude boost to dark matter annihilation signals, and prospects for detecting local substructure in cold dark matter. Next, I will show how enhanced primordial perturbations can form halos during the radiation era, with densities sufficient to be probed by microlensing. I will then discuss results from a new simulation of primordial black hole dark matter, which shows that N-body interactions reshape gravitational-wave predictions while producing collisional heating that suppresses structure up to galactic scales.
