Bitcoin

Bitcoin is an open, permissionless peer-to-peer electronic cash network and the first widely used decentralized crypto asset. Its goal is to let any two parties transfer value directly over the internet without going through a bank or payment company.

"Bitcoin" usually refers to two things at once: the Bitcoin network and protocol run by nodes around the world, and BTC, the network's native asset. The network records and validates every transaction; BTC is the unit of value that moves across it and is also used to pay transaction fees. No company or foundation controls the network — its rules are enforced collectively by the participants who run the software.

Before Bitcoin, online payments almost always relied on a trusted third party — a bank or card network — to keep the ledger and prevent the same money from being spent twice, the "double-spending problem". The whitepaper argues that this trust-based model brings transaction costs, reversibility and dependence on intermediaries.

Bitcoin's answer is to bundle transactions into blocks in time order and link them into a public chain secured by proof of work. Nodes follow the valid chain with the most accumulated work, so participants who do not trust each other can still agree on transaction order and double spending is prevented.

This does not mean Bitcoin removes every intermediary or risk: many users still access BTC through exchanges, custodians or wallet services, and confirmed on-chain transactions are generally irreversible, with none of the recourse that traditional finance offers when mistakes or theft occur.

At the heart of Bitcoin is a public ledger — the blockchain — kept by every full node.

• Transactions: users sign with their private keys to spend previously received "unspent transaction outputs" (UTXOs), creating new outputs for the recipient.
• Nodes: full nodes independently download and validate every transaction and block, rejecting anything that breaks the consensus rules (such as a double spend or excess issuance).
• Miners and blocks: miners bundle pending transactions into a block and repeatedly compute SHA-256 hashes, searching for a result below the target difficulty — this is proof of work.
• Confirmation: the miner who finds a valid block broadcasts it; other nodes validate it and extend the chain. Each further block adds a "confirmation" and makes the transaction harder to rewrite.
• Difficulty adjustment: every 2,016 blocks the network retargets mining difficulty so that blocks arrive roughly every 10 minutes on average.

For deeper technical detail, see the material under Whitepaper & Technical Documentation below.

Bitcoin was created by a person or group using the pseudonym Satoshi Nakamoto. On October 31, 2008, Satoshi published the whitepaper "Bitcoin: A Peer-to-Peer Electronic Cash System" on a cryptography mailing list, mined the genesis block on January 3, 2009, and released the first software, Bitcoin v0.1, in January 2009.

Satoshi's real identity has never been verified, and this page does not adopt any identity theory. Satoshi gradually withdrew from public discussion around the end of 2010; since then the software has been maintained by an open-source developer community, with the reference implementation now called Bitcoin Core. Anyone can review the code or propose improvements, but changes to protocol rules require broad acceptance by network participants.

• October 31, 2008: Satoshi Nakamoto publishes the Bitcoin whitepaper.
• January 3, 2009: the genesis block (height 0) is created.
• January 2009: Bitcoin v0.1 is released; on January 12, block 170 contains the first transfer, from Satoshi to Hal Finney.
• November 28, 2012: first halving (block 210,000) — the block subsidy falls from 50 to 25 BTC.
• July 9, 2016: second halving (block 420,000) — down to 12.5 BTC.
• August 24, 2017: Segregated Witness (SegWit, BIP 141 and related) activates at block 481,824.
• May 11, 2020: third halving (block 630,000) — down to 6.25 BTC.
• November 14, 2021: the Taproot upgrade (BIPs 340/341/342) activates at block 709,632.
• April 20, 2024: fourth halving (block 840,000) — down to 3.125 BTC.

All dates are UTC; block heights and times can be checked in a block explorer.

• Pre-set issuance: new coins are issued only through the block subsidy, which halves roughly every 210,000 blocks, with total supply capped at just under 21 million — no central party can issue more at will.
• Proof-of-work security: blocks are produced through competition for hash power, so rewriting history requires enormous computing and energy cost; the trade-off is that mining itself consumes a lot of electricity.
• Permissionless validation: anyone can run a full node and independently verify the entire history and rules without trusting anyone else.
• Longest-running crypto network: in continuous operation since 2009, with open-source code that has been publicly reviewed for many years.
• Conservative protocol evolution: rule changes are usually activated as backward-compatible soft forks after years of discussion — stable, but slow to add new features.

• The native monetary asset of the Bitcoin network, transferred peer to peer between users.
• Paying on-chain transaction fees, which go to the miner who includes the transaction.
• Rewarding miners (block subsidy plus fees), giving them an incentive to secure the network.
• Held as a long-term asset by some users and institutions — a market behavior, not a protocol function.
• Smaller, faster payments through second-layer protocols such as the Lightning Network.

BTC is not a governance token and holding it confers no voting rights; Bitcoin also has no native proof-of-stake (PoS) staking.

Bitcoin's security rests on several parts working together:

• Proof of work: to rewrite confirmed history, an attacker must redo the work of those blocks and every block after them, and outpace the honest network.
• Chain selection: nodes follow the valid chain with the most accumulated work, not simply the longest chain.
• Full nodes: nodes enforce all rules independently, so they reject a rule-breaking block (such as one creating excess coins) even if a miner produced it.
• Economic incentives: the subsidy and fees make honest mining more profitable than attacking the network.
• Difficulty adjustment: even when hash power changes sharply, the block interval is pulled back toward about 10 minutes.

These mechanisms rest on assumptions: the whitepaper's security model assumes honest nodes control most hash power. Whoever controlled a majority could in principle censor transactions or reorganize recent blocks (a "51% attack"), and the concentration of mining and mining pools is a long-standing concern. Bitcoin is not immune to attack; its security depends on ongoing economic and technical conditions.

Several categories of infrastructure have grown up around Bitcoin:

• Wallets: self-custody software and hardware wallets, as well as custodial wallet services.
• Node software: Bitcoin Core is the most widely used reference implementation; other implementations also exist.
• Mining: hardware manufacturers, mining operations and mining pools.
• Trading and custody: centralized exchanges, brokers and institutional custodians.
• Second layers and payments: protocols such as the Lightning Network for faster, smaller payments.
• Developer infrastructure: block explorers, libraries, the BIP process and test networks.

These services are run by separate, independent teams with different risks and levels of trust, and should be assessed individually.

• Peer-to-peer value transfer: sending value between users, including across borders, without a bank account; actual cost and speed depend on network congestion.
• Settlement: once sufficiently confirmed, on-chain transactions are very hard to reverse, which suits final settlement of larger amounts.
• Payments: some merchants accept BTC, with small payments mostly made over the Lightning Network.
• Long-term holding: some individuals and institutions hold BTC as a long-term asset — a market choice, not something the protocol guarantees.
• Financial infrastructure: BTC is also used as the underlying asset or collateral for some financial products; these are offered by third parties and carry risks separate from the Bitcoin protocol.

• Limited base-layer throughput: block size and the ~10-minute block interval mean far fewer on-chain transactions per second than large payment networks.
• Confirmation takes time: transactions usually wait for several block confirmations, and larger amounts often wait longer.
• Fee variability: fees can rise sharply when the network is congested.
• Energy use: proof-of-work mining needs a lot of electricity — part of its security model, and the subject of environmental debate.
• Limited programmability: Bitcoin Script is deliberately simple, so complex smart-contract functionality is more limited than on platforms such as Ethereum.
• Key-management burden: self-custody requires safely storing private keys or seed phrases; once lost, they usually cannot be recovered.

The risks below are for understanding only and are not investment advice.

• Market risk: BTC is highly volatile and can fall sharply in a short time.
• Regulatory risk: laws, taxes and trading restrictions for crypto assets differ between countries and may change.
• Custody and key risk: lost or stolen keys, or failure of a custodial platform, can make assets unrecoverable.
• Protocol and software risk: software bugs, implementation flaws or contentious rule changes could affect the network.
• Mining concentration and security assumptions: concentrated hash power or pools could enable censorship or reorganizations; security relies on continuing economic incentives.
• Fee-market uncertainty: whether fees can sustain network security as the block subsidy keeps shrinking is still an open question.
• Competition and substitution: other blockchains or payment methods may replace Bitcoin for some uses.
• Liquidity and market-structure risk: failures at exchanges, derivatives venues or third-party products can amplify price swings.

Bitcoin has no company-set roadmap. Protocol improvements are usually discussed publicly as Bitcoin Improvement Proposals (BIPs), implemented by open-source projects such as Bitcoin Core, and activated as soft forks only after broad adoption by nodes and miners.

• Activated: Segregated Witness (SegWit, 2017) and Taproot (2021).
• Proposed, not activated: for example BIP 119 (CHECKTEMPLATEVERIFY) and BIP 347 (OP_CAT), "covenant" proposals on which the community still disagrees about whether and how to activate.

Being in the BIPs repository does not mean a proposal will be activated. Last checked: October 4, 2026.