What exactly is a physical bitcoin? In short, they are real metal coins, and some of them hold the private keys that control digital bitcoins (or other crypto-currencies). Often, these private keys are behind tamper-proof hologram stickers. The coins are collectible, and some of them are very valuable, up to millions of dollars each. They were originally created as educational tools, and are interesting to study because they are physical artifacts of the blockchain revolution. This page is dedicated to them.