Bitcoin (BTC)

Bitcoin is a digital money that people can send directly to each other over the internet, without a bank in the middle. Instead of one company keeping the records, thousands of computers around the world keep identical copies of a shared record book called the blockchain.

Bitcoin was the first cryptocurrency, and most later projects borrowed ideas from it.

Bitcoin was described in a nine-page paper, “Bitcoin: A Peer-to-Peer Electronic Cash System” (opens in a new tab), published on October 31, 2008, by someone using the name Satoshi Nakamoto. Nobody has publicly proven who Satoshi is, and Satoshi stopped posting publicly around 2010–2011.

The paper's goal was a way to send payments online that didn't rely on trusting a bank or payment company, and that solved the problem of the same digital money being spent twice.

1. October 31, 2008

   The Bitcoin paper is published.

2. January 3, 2009

   The first block (the “genesis block”) is created, starting the network.

3. May 22, 2010

   A programmer pays 10,000 bitcoins for two pizzas, often called the first real-world purchase.

4. 2012, 2016, 2020, 2024

   The four “halvings” so far, each cutting the new-bitcoin reward for miners in half. The most recent was in April 2024.

5. 2017 and 2021

   Major software upgrades (SegWit in 2017, Taproot in 2021) improve capacity and flexibility.

6. September 2021

   El Salvador makes bitcoin legal tender. It later changed the law in 2025 so businesses are no longer required to accept it.

7. January 10, 2024

   The U.S. SEC approves the listing of spot bitcoin exchange-traded products.

Imagine a public ledger, like a church's offering record, that everyone can see and check, but nobody can secretly erase. Every few minutes a new page (a block) is added, listing recent payments. Each page is linked to the one before it, forming a chain.

Computers called miners compete to add the next page. They do this by solving a hard number puzzle, which takes real electricity and equipment. The winner adds the block and receives newly created bitcoin plus fees. This is called proof of work.

Because rewriting old pages would require redoing all that work faster than the rest of the network, the record becomes very hard to change over time.

People often write Bitcoin with a capital B for the network and software, and bitcoin (or BTC) with a small b for the units of money. So you might say “the Bitcoin network moves bitcoin.”

Bitcoin is known for its fixed maximum supply of 21 million coins, set in the software. No company or government can decide to print more. That scarcity is a key reason some people compare it to digital gold. It does not mean the price must go up.

One bitcoin can be split into 100 million smaller units called satoshis, so you don't need a whole bitcoin to use it.

• It was the first cryptocurrency and has the longest track record.
• Its supply is capped at 21 million, set in the software.
• It is secured by proof-of-work mining, which uses significant electricity.
• Its design focuses on being money; it has more limited programming features than networks like Ethereum.

• 1

  The first Bitcoin block includes a newspaper headline from that day: “Chancellor on brink of second bailout for banks.”

• 2

  May 22 is celebrated by fans as “Bitcoin Pizza Day,” after the 10,000-bitcoin pizza purchase in 2010.

• 3

  The smallest unit of bitcoin, one hundred-millionth of a coin, is named a “satoshi” after Bitcoin's creator.

• Myth: Bitcoin is anonymous.

  Fact: Every transaction is public on the blockchain. Addresses don't show names, but they can often be traced, especially through exchanges that verify identity.

• Myth: Someone controls Bitcoin and can reverse my payment.

  Fact: No company runs Bitcoin, and payments can't be reversed by a customer service desk.

• Myth: You need to buy a whole bitcoin.

  Fact: Bitcoin can be divided into tiny pieces called satoshis.

Specific to Bitcoin

• Bitcoin's price has historically been very volatile.
• Scammers often ask victims to pay “fees,” “taxes,” or “fines” in bitcoin, including through bitcoin ATMs. Government agencies and real businesses don't demand payment this way.
• Mining uses large amounts of electricity, which raises environmental and policy debates.

For every cryptocurrency

• Prices can rise or fall sharply, sometimes within hours. Only people who can afford to lose the money should consider buying any cryptocurrency, and CLC does not recommend buying, selling, or holding any.
• Transactions usually can't be reversed. If you send to the wrong address, or to a scammer, the money is usually gone.
• Whoever controls the keys controls the coins. Anyone who learns your recovery phrase can take everything. No real company or helper will ever ask for it.
• Scammers use well-known names. Fake giveaways, “guaranteed returns,” and impersonated celebrities or companies are common. Learn the warning signs in our Resource Center.
• Rules differ by country and can change. Taxes may apply when you sell or spend cryptocurrency.

Block

A batch of recent transactions added to the blockchain.

Mining

Using computers to secure the network and add blocks, in exchange for new bitcoin and fees.

Proof of work

A security method where adding a block requires costly computing work.

Halving

The scheduled cut in the miners' reward, about every four years.

Satoshi

The smallest unit of bitcoin: 0.00000001 BTC.

Wallet

An app or device that holds the keys used to control your bitcoin.

Company and project sources describe their own products; we cite them for what the products do, not as endorsements. Last reviewed October 19, 2026.

• Bitcoin: A Peer-to-Peer Electronic Cash System (opens in a new tab)Satoshi Nakamoto, 2008
• How Bitcoin works (opens in a new tab)Bitcoin.org
• Block chain guide (opens in a new tab)Bitcoin developer documentation
• Statement on spot bitcoin ETPs (opens in a new tab)U.S. SEC, January 10, 2024
• Lightning Network (opens in a new tab)Project site
• Crypto asset (glossary) (opens in a new tab)Investor.gov (U.S. SEC)