Abstract：Strong gravitational lensing is the convergence of multiple light beams from a source object by the gravity of an intervening lens object. This rare but fascinating phenomenon has allowed us to probe baryons, dark matter, and cosmology. In this talk, I will show several observational examples of how strong gravitational lensing events can be used to explore galaxy evolution and the nature of dark matter, and also describe an ongoing project of measuring the Hubble constant with strongly-lensed supernovae.