What is Bitcoin, and how does it work without a bank in charge?
Bitcoin was the first cryptocurrency and is still the reference point for the rest. This profile sticks to what its founding documents and official sources actually say.
Education only, not investment, tax or legal advice. Crypto-assets are high-risk — risk disclosure.
BTCThe short answer
Bitcoin is a digital currency that runs on a public network of computers instead of a bank. Its ledger, the blockchain, is kept in agreement by proof of work, and its rules limit the total supply to 21 million coins, released on a fixed, shrinking schedule.
Key takeaways
- Bitcoin was described in a 2008 paper by the pseudonymous Satoshi Nakamoto, and its software was first released in January 2009.
- Miners compete to add blocks using proof of work; the network accepts the chain with the most accumulated work.
- New coins enter circulation through mining, and the reward halves every 210,000 blocks until issuance stops at a total of 21 million.
- Transactions are public and irreversible once confirmed, so mistakes and theft are very hard to undo.
- U.S. regulators treat bitcoin as a commodity and have warned that it is speculative and volatile.
What is Bitcoin and who created it?
Bitcoin is two things with the same name. Bitcoin (capital B) is a network of computers that share one public ledger. bitcoin (lower case, ticker BTC) is the money recorded on it, which anyone on the network can send without a bank's approval.
The design comes from a short paper titled Bitcoin: A Peer-to-Peer Electronic Cash System, signed by Satoshi Nakamoto1. Nakamoto announced it on a cryptography mailing list on 31 October 20082 and released the first version of the software on 8 January 20093. None of these documents gives a real-world identity behind the name.
The paper's aim was simple to state: let people pay each other online without a trusted middleman, while stopping anyone from spending the same coin twice1. No company owns the network. Bitcoin's own FAQ compares it to email, which nobody owns either5. The main software, Bitcoin Core, is open source and its code is public on GitHub4.
How does Bitcoin agree on one version of the ledger?
Many independent computers (called nodes) each keep a full copy of the ledger. New transactions are grouped into blocks. To add a block, a miner must find a number that makes the block's digital fingerprint (its hash) fall below a target. Finding it takes huge numbers of guesses, but checking it takes a moment. This is proof of work1.
How a payment gets into the ledger
- 1
Payment sent
The owner signs the payment with their private key and broadcasts it.
- 2
Shared with nodes
Nodes check it follows the rules and hold it with other waiting payments.
- 3
Miners compete
Miners bundle payments into a candidate block and keep guessing until its hash falls below the target.
- 4
Block added
The winner shares the block; other nodes check the work and add it to their copy.
- 5
Confirmations pile up
Each later block makes the payment harder to undo.
If two versions of the chain appear, nodes follow the one with the most proof of work behind it. The whitepaper argues that this stays safe as long as honest participants control most of the computing power, because an attacker would have to redo all that work faster than everyone else1.
The pace is managed automatically. The software targets one block every ten minutes4. Every 2,016 blocks, nodes compare how long those blocks actually took with the ideal of 1,209,600 seconds (two weeks) and make the puzzle harder or easier to match6.
How many bitcoins will there ever be?
New coins are created only as a reward for the miner who adds a block. By convention, the first transaction in each block pays that reward to the block's creator1. The reward is cut in half every 210,000 blocks, a rule written into the Bitcoin Core code4. Bitcoin.org describes the result: issuance shrinks over time and stops completely once 21 million bitcoins exist5.
Nakamoto spelled out the plan when releasing the software: total circulation of 21,000,000 coins, with the amount cut in half every four years3. The same message listed the first four stages:
Planned issuance in the first four reward eras, as listed in the January 2009 release announcement Source: [3]
| Era | New coins in the era | Running total |
|---|---|---|
| 1st | 10,500,000 | 10,500,000 |
| 2nd | 5,250,000 | 15,750,000 |
| 3rd | 2,625,000 | 18,375,000 |
| 4th | 1,312,500 | 19,687,500 |
Worked example
Why "every 210,000 blocks" means about every four years
At the target of one block every 10 minutes, 210,000 blocks take 2,100,000 minutes, or about 3.99 years. Real block times wander around the target, so the actual dates drift. After the four eras above, 93.75% of the 21 million limit would already be issued; later eras add ever smaller amounts. Our halving explainer goes further.
What is bitcoin used for?
The original purpose was online payments sent directly between two people1. Today people also use bitcoin to move value across borders, to hold as a long-term asset and to trade. In the U.S., the SEC approved the listing of several spot bitcoin exchange-traded products (ETPs) on 10 January 2024, while stating that it did not approve or endorse bitcoin itself7.
Bitcoin compared with a bank transfer
| Question | Bank transfer | Bitcoin |
|---|---|---|
| Who approves it? | Your bank and the payment system | Network rules checked by every node |
| Can it be reversed? | Sometimes, through the bank | No, once confirmed; only the receiver can send it back |
| Who can see it? | You, the banks and authorities | Anyone, on a public ledger |
| What if you lose access? | The bank can verify you and restore access | No one can restore lost keys |
Bitcoin is not anonymous. Its FAQ says that using it leaves extensive public records5. Addresses are not printed with names, but the full history of every address can be read by anyone.
What are the key dates in Bitcoin's history?
Figure · Bitcoin: key dates
- Oct 2008Whitepaper
- Jan 2009Genesis block mined
- Nov 2012First halving
- Nov 2021Taproot activates
- Jan 2024Spot ETPs approved
- Apr 2024Fourth halving
Bitcoin milestones (block dates in UTC, from block timestamps)
| Date | Milestone |
|---|---|
| 31 Oct 2008 | Whitepaper announced2 |
| 3 Jan 2009 | Genesis block mined4 |
| 8 Jan 2009 | First software release (v0.1)3 |
| 28 Nov 2012 | First halving, block 210,00010 |
| 9 Jul 2016 | Second halving, block 420,00010 |
| 11 May 2020 | Third halving, block 630,00010 |
| 14 Nov 2021 | Taproot upgrade activates at block 709,6329410 |
| 10 Jan 2024 | SEC approves spot bitcoin ETPs7 |
| 20 Apr 2024 | Fourth halving, block 840,00010 |
The very first block, the genesis block, carries a timestamp of 3 January 2009 and embeds a newspaper headline: "The Times 03/Jan/2009 Chancellor on brink of second bailout for banks"4. Taproot, which added a new signature scheme, was scheduled for block 709,6329, the height Bitcoin Core's code still records as its activation point4.
What are the specific risks of holding bitcoin?
- Price swings. Bitcoin's own FAQ warns that relatively small events can move its price a lot5. SEC Chair Gary Gensler called it primarily a speculative, volatile asset in 20247.
- Irreversible mistakes. A confirmed payment cannot be cancelled. Send to the wrong address and only the receiver can return it5.
- Theft and fraud. The CFTC warns that virtual currencies are commonly targeted by hackers and fraudsters and that there may be no recourse if they are stolen8.
- Weak protections. The CFTC treats bitcoin as a commodity but describes the market overall as largely unregulated8. Some countries restrict or ban its use5.
- Illicit use. The SEC has noted that bitcoin is also used for ransomware, money laundering and sanctions evasion7.
Risk warning
Only risk what you can afford to lose
Bitcoin can fall sharply in value, and lost or stolen coins are usually gone for good. Nothing on this page is investment advice. Read our risk disclosure and our guide to wallets and private keys before buying any.
What mistakes do beginners make with bitcoin?
Common beginner mistakes
Thinking bitcoin is anonymous
Every transaction is recorded on a public ledger forever. Treat your activity as traceable.
Leaving keys where others control them
Coins held on a platform depend on that platform staying solvent and honest. Learn how custody works before choosing where to keep them.
Saving recovery words in the cloud
Anyone who sees your recovery phrase can take your coins. Keep it offline and never type it into a website or share it with "support" staff.
Sending a test amount only after the big one
Because payments cannot be reversed, send a small amount first and check it arrived before moving larger sums.
Frequently asked questions
Can the 21 million limit be changed?
The limit is a rule in the Bitcoin Core software4. Changing it would mean persuading the people who run nodes to switch to different software with a different rule.
How long does a bitcoin payment take?
The network aims for one new block about every ten minutes4, so a payment usually gets its first confirmation within minutes. Many recipients wait for a few more blocks before treating a large payment as final.
Is bitcoin legal?
It depends on where you live. Bitcoin.org notes that most jurisdictions have not banned it but some restrict or prohibit its use5. In the United States the CFTC treats it as a commodity8. Our Policy section covers the rules by region.
What happens when all 21 million bitcoins are issued?
Miners would then be paid only through transaction fees, which the whitepaper described as the long-run incentive once new coins stop1.
The bottom line
Bitcoin is a shared public ledger kept honest by proof of work, with a supply rule that stops at 21 million coins. Those rules are well documented. They do not protect you from price swings, scams, lost keys or mistaken payments, so learn how custody and wallets work before you hold any.
Sources
- Bitcoin: A Peer-to-Peer Electronic Cash System — Satoshi Nakamoto (hosted at bitcoin.org), 2008 Primary source
- Bitcoin P2P e-cash paper (mailing list announcement) — Satoshi Nakamoto, Cryptography mailing list (metzdowd.com), 2008 Primary source
- Bitcoin v0.1 released (mailing list announcement) — Satoshi Nakamoto, Cryptography mailing list (metzdowd.com), 2009 Primary source
- Bitcoin Core source code: src/kernel/chainparams.cpp — Bitcoin Core project (GitHub), 2026 Primary source
- Frequently Asked Questions — bitcoin.org Primary source
- Block Chain (Bitcoin Developer Guide) — developer.bitcoin.org Primary source
- Statement on the Approval of Spot Bitcoin Exchange-Traded Products — U.S. Securities and Exchange Commission (Chair Gary Gensler), 2024 Primary source
- What is Bitcoin? (Bitcoin Basics) — U.S. Commodity Futures Trading Commission, Office of Customer Education and Outreach Primary source
- Bitcoin Core 0.21.1 release notes — bitcoincore.org, 2021 Primary source
- Bitcoin block data for heights 210,000, 420,000, 630,000, 709,632 and 840,000 (read 2 October 2026) — mempool.space block explorer API (cross-checked with Blockstream Explorer), 2026 Primary source
How we checked this page: every figure above links to the numbered source it came from. Spotted an error? Tell the desk — see our editorial policy.
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