Bitcoin is digital money that anyone can send to anyone else over the internet, with no bank or company in the middle, and with a total supply that is fixed at 21 million coins.
That is the one-sentence answer. The rest of this page unpacks each piece of it, so that by the end the sentence makes sense rather than just sounding impressive.
Money you can send over the internet without a bank
When you send dollars to a friend with a banking app, your bank lowers the number in your account and raises the number in theirs. The bank keeps the record, and you trust it to keep that record honestly.
Bitcoin does the same job with no bank. Instead of one company keeping the record, thousands of computers around the world keep identical copies of it and check each other’s work. If you send bitcoin to a friend in another country at 3 a.m. on a Sunday, it arrives in minutes, and nobody had to approve it.
That is why people call bitcoin “peer to peer.” The money goes directly from you to the other person, the way cash does when you hand it over, except it works at any distance.
What a blockchain is
The shared record is called the blockchain. Think of it as a public ledger, a running list of every bitcoin transaction ever made, that anyone in the world can download and check.
Transactions are bundled into groups called blocks. A new block is added roughly every ten minutes, and each block is mathematically linked to the one before it, forming a chain. Changing an old block would break every link after it, which is why the history is so hard to tamper with.
Because the ledger is public, you can verify that a payment happened without taking anyone’s word for it. That is the core trick: bitcoin replaces trust in an institution with something you can check for yourself.
Who runs it
Nobody, and everybody. There is no Bitcoin headquarters, CEO, or customer service line. The network is run by volunteers and businesses that play two roles.
Nodes are computers that store a full copy of the blockchain and check every transaction against the rules. Anyone with a laptop and some patience can run one. If a transaction breaks the rules, for example by spending bitcoin someone does not have, nodes simply reject it.
Miners are the computers that add new blocks. They compete to solve a hard math puzzle, and the winner gets to add the next block and collect a reward of newly created bitcoin plus the fees from the transactions inside. This process is called mining, and the puzzle is what makes rewriting history impractically expensive.
The rules themselves are written in open-source software that anyone can read. Changing the rules requires broad agreement among the people who run nodes, which is why Bitcoin changes slowly and cautiously.
Why there will only ever be 21 million
The software creates new bitcoin on a fixed schedule as mining rewards, and that schedule was set in 2009 and has never been changed. Roughly every four years the reward is cut in half, an event called the halving.
The reward started at 50 bitcoin per block. After the fourth halving in April 2024 it is 3.125 bitcoin per block. The 20 millionth bitcoin was mined in March 2026, and the remaining coins will trickle out more and more slowly until the last fraction is mined around the year 2140.
No government or company can print more. That fixed supply is the main reason people compare bitcoin to gold and treat it as a long-term savings asset rather than just a payment tool.
What “a bitcoin” is, and buying a fraction
A bitcoin is a unit on the ledger, nothing more. There is no coin, file, or object; there is only a record saying that a certain amount belongs to a certain address.
You do not need to buy a whole one. Each bitcoin divides into 100 million smaller units called satoshis, or “sats,” named after bitcoin’s creator. You can buy ten dollars’ worth on most exchanges, and that purchase will be recorded as some number of satoshis.
Keys and wallets
The one paragraph you need
Every bitcoin address has a matching pair of keys. The public key is like your account number: you share it so people can pay you. The private key is like the signature that authorizes a payment: whoever holds it can spend the bitcoin, so it must never be shared. A wallet is the app or device that holds your keys and creates transactions for you. If you use an exchange, it holds the keys on your behalf; if you hold your own wallet, you hold them yourself. We cover that choice in Wallets and Self-Custody.
What bitcoin is not
- Not a company. There is no stock, no earnings report, and no one who can shut it down or change your balance.
- Not a stock. Owning bitcoin does not entitle you to a share of anything. Its value comes from what people are willing to pay for a scarce, portable, hard-to-censor form of money.
- Not anonymous. Addresses are not tied to names, but every transaction is public forever, and analysis firms are very good at linking addresses to people. Bitcoin is better described as pseudonymous.
Common misconceptions
“Bitcoin is backed by nothing.” It is not backed by a government, but neither is gold. It is backed by the rules of the network, the energy miners spend to secure it, and the people who choose to use it.
“Bitcoin has been hacked.” Exchanges and individuals have been hacked, often badly. The Bitcoin network itself has never had its ledger successfully altered since it launched in 2009.
“It’s only used by criminals.” Criminals use bitcoin, as they use cash and banks. Because the ledger is public, it is often easier to trace than cash, which is one reason law enforcement has recovered large sums from it.
“Bitcoin and crypto are the same thing.” Bitcoin was the first and is the largest, but thousands of other coins exist with very different designs, teams, and risks. See What Is Ethereum? and Other Coins.
The honest risks
Price swings. Bitcoin’s price has risen enormously over its lifetime, and it has also fallen by half or more several times, including a drop of roughly 50 percent between October 2025 and February 2026. Anyone who buys should expect big moves in both directions.
Losing your keys. There is no password reset. If you hold your own keys and lose them, the bitcoin is gone. If an exchange holds them and it fails, you become a creditor in a bankruptcy, as customers of Mt. Gox and FTX learned.
Scams. Because transactions cannot be reversed, bitcoin attracts fraud: fake investment platforms, impersonators, and “send one, get two back” offers. Keeping Your Bitcoin Safe covers the patterns to watch for.
Key point: Bitcoin is a public ledger with a fixed supply that nobody controls. Its strengths and its risks come from the same fact: you are in charge, and there is no one to call.
Next
- A Short History of Bitcoin: where it came from and how it survived.
- How Bitcoin Is Used Today: saving, payments, and who holds it.
- How to Buy Bitcoin: a step-by-step first purchase.