Bitcoin (BTC) is a decentralized, peer-to-peer digital currency that allows users to send and receive value directly, without banks or other intermediaries. It was introduced on October 31, 2008, when a pseudonymous person or group using the name Satoshi Nakamoto published the whitepaper "Bitcoin: A Peer-to-Peer Electronic Cash System." Bitcoin's mainnet launched in January 2009, making it the first cryptocurrency and the origin of blockchain technology as it's used today.
Bitcoin runs on its own blockchain, a public, distributed ledger maintained by a global network of computers rather than a central authority. Transactions are verified and secured through proof-of-work (PoW) mining, in which computers compete to solve cryptographic puzzles using the SHA-256 algorithm. Once a transaction is confirmed on the blockchain, it becomes effectively permanent and cannot be altered or reversed, which is what gives Bitcoin its security and censorship resistance.
Bitcoin's supply is capped at 21 million coins by protocol rule, with new BTC issued to miners through a block reward that halves roughly every four years. As of June 2026, about 20.05 million BTC were in circulation, with a market cap of roughly $1.18 trillion, ranking #1 among cryptocurrencies, according to CoinGecko and CoinMarketCap. Bitcoin's launch inspired thousands of other cryptocurrencies, but it remains the largest and most widely held digital asset by market capitalization.