Collectible coins are items sought after by numismatists and collectors, often due to their rarity, historical significance, or unique features. In the United States, the 25-cent coins, or quarters, are particularly popular, especially those included in Proof Sets, which are produced with a special minting process that results in a higher quality finish. The 2005 Proof Sets feature quarters that were part of the State Quarters Program, showcasing designs representative of each of the 50 states. These sets are valued for their aesthetic appeal, low mintage, and inclusion of additional collectible coins, making them attractive to collectors.