The United States National Gem Collection at the Smithsonian Institution is well-known for its many world-class gems and jewelry pieces such as the notorious Hope Diamond, 423 carat Logan Sapphire, Napoleon Diamond Necklace, and the recently acquired Carmen Lúcia Ruby, but among the more than 10,000 other gems are many equally unique and fascinating stones from around the world. This talk will explore the science and lore of some of the famous and lesser known gems in the National Collection, as well as highlight recent research on the cutting history and luminescence properties of the Hope Diamond.