The 1999 United States Mint Proof Set includes coins with a copper-plated zinc and copper-nickel composition, struck in proof condition at the San Francisco Mint. This set comes in its original box with a Certificate of Authenticity from the U.S. Mint, guaranteeing the coins' authenticity and quality. As an uncirculated set from the United States, it is a valuable collectible for coin enthusiasts and collectors looking for pristine coins from the late 20th century.