What is Bitcoin?

Bitcoin was the first cryptocurrency, launched in 2009 by an unknown person or group using the name Satoshi Nakamoto. It lets people send value to each other over the internet without a bank in the middle.

Only 21 million bitcoin will ever exist. New coins are released to the computers, called miners, that secure the network, and the number released halves roughly every four years. That fixed supply is why some people compare Bitcoin to digital gold.

Bitcoin's price moves sharply. It has risen and fallen by more than half within a single year several times, so it is a risky place to keep money you may need soon. It is also pseudonymous rather than anonymous: every transaction is public on the blockchain, and investigators can often trace who is behind an address.

Running the Bitcoin network uses a great deal of electricity. The Cambridge Centre for Alternative Finance publishes a live estimate of how much.