$BTC Bitcoin (abbreviation: BTC; sign: ₿) is the first decentralized cryptocurrency. Based on a free-market ideology, bitcoin was invented in 2008 when an unknown entity published a white paper under the pseudonym of Satoshi Nakamoto.[5] Use of bitcoin as a currency began in 2009,[6] with the release of its open-source implementation.[7]: ch. 1  In 2021, El Salvador adopted it as legal tender.[4] As bitcoin is pseudonymous, its use by criminals has attracted the attention of regulators, leading to its ban by several countries as of 2021.[8]