Bitcoin (abbreviation: BTC[a] or XBT;[b] sign: ₿) is the first decentralized cryptocurrency. Nodes in the bitcoin network verify transactions through cryptography and record them in a public distributed ledger called a blockchain. Based on a free market ideology, bitcoin was invented in 2008 by Satoshi Nakamoto, an unknown person.[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] Bitcoin is currently used less as a medium of exchange and more as a store of value. It is mostly seen as an investment and has been described by many scholars as an economic bubble.[8]
As bitcoin is pseudonymous, its use by criminals has attracted the attention of regulators, leading to its ban by 51 countries as of 2021.[9][10] The environmental effects of bitcoin are also substantial.[11] Its proof-of-work algorithm for bitcoin mining is computationally difficult and requires increasing quantities of electricity,[12] so that, as of 2022, bitcoin is estimated to be responsible for 0.2% of world greenhouse gas emissions.[13]