Dark matter makes up about 85% of the matter content of the Universe, yet its fundamental nature remains one of the major open questions in physics. While many dark matter models predict similar large-scale cosmic structure, they can produce distinct signatures on sub-galactic scales (~kpc), making small-scale structure a powerful probe of dark matter physics. In this talk, I will discuss how dark matter halos and their substructure can be modeled using carefully calibrated semi-analytic and empirical approaches, and how these predictions can be tested with strong gravitational lensing. I will then present new constraints on dark matter derived from a sample of 28 quadruply imaged strong-lens systems recently observed with JWST.
