Switchable mirrors based on rare earth hydrides were discovered in my laboratory in 1994. PhD student J.N. Huiberts observed a reversible metal-to-insulator transition when a thin film (150 to 500 nm) of yttrium or lanthanum coated with a thin layer of palladium was exposed to hydrogen gas. The transition accompanies conversion of a metallic dihydride phase to a semiconducting trihydride. Since then, our group has carried out fundamental research that has elucidated many important aspects of switchable mirror phenomena. This talk will include demonstrations of the spectacular changes in optical properties in rare earth hydride films, and describe transport (electrical conductivity, Hall coefficient, magnetoresistance, diffusion, electromigration), and optical measurements. Predictions of theoretical models (band structure, strong electron correlation) proposed recently to explain the metal-insulator transition in these hydrides, will be compared to recent experiments. Beside these remarkable optical and electrical properties we have also discovered recently that epitaxial YHx films exhibit unusual structural properties that open the way to pixel-by-pixel switching. Finally, I shall briefly describe the first all-solid-state device based on a switchable mirror and new rare-earth-free switchable mirrors discovered at LBNL. In addition to the shiny metal-to-transparent transition, these switchable films exhibit a remarkable black state that may find applications in buildings.