A Permanent Record Book
Every Bitcoin transaction that has ever happened is recorded in a single shared file called the blockchain. Think of it as a public ledger — a record book that tracks who sent Bitcoin to whom, how much, and when. Once something is written in this book, it stays there forever. No one can erase a page, change a number, or tear out an entry.
What makes the blockchain different from a traditional record book is that no single person or company keeps it. Thousands of computers around the world — called nodes — each hold a complete, identical copy. Every time a new entry is added, every copy updates at the same time. There is no central server to hack, no database administrator to bribe, and no single point of failure. If one computer goes offline, the other thousands still have the full record.
This is the foundation that makes Bitcoin work without banks. Instead of trusting a company to track your balance honestly, you trust a system where everyone can verify everything.
How Blocks Build the Chain
Transactions do not get added to the blockchain one at a time. Instead, they are bundled into groups called blocks. A new block is added approximately every ten minutes.
Here is how it works:
- When you send Bitcoin, your transaction goes into a waiting area along with other pending transactions.
- Miners collect these transactions and package them into a candidate block. Each block holds around 2,000 to 4,000 transactions.
- Miners compete to solve a computational puzzle — a process called proof of work. The first miner to find the solution earns the right to add their block to the chain.
- The winning block is broadcast to the network. Other nodes verify that every transaction in the block is valid and that the puzzle was solved correctly.
- Once verified, the block is permanently added to the chain.
Each block contains a mathematical fingerprint of the previous block, linking them together in a strict sequence. This is where the name “blockchain” comes from — a chain of blocks, each pointing back to the one before it.
This linking is what makes the blockchain tamper-proof. If someone tried to alter a transaction in an old block, the fingerprint would change, breaking the link to every block that came after it. The attacker would need to redo the work for that block and every subsequent block — faster than the rest of the network combined. With hundreds of thousands of blocks already in the chain and the massive computing power securing it, this is practically impossible.
Why No One Can Cheat
The blockchain solves a problem that stumped computer scientists for decades: how do you get thousands of strangers on the internet to agree on a shared record without anyone in charge?
Bitcoin’s answer combines three ideas:
Transparency. The blockchain is public. Anyone can view any transaction ever made. You do not need permission or an account. This openness means everyone can independently verify that the rules are being followed.
Distribution. The ledger is not stored in one place. Thousands of nodes across the globe each maintain a full copy. To change the record, you would need to alter the majority of these copies simultaneously — a feat that has never been achieved in Bitcoin’s history.
Proof of work. Adding a new block requires real computational effort and real energy. This makes it expensive to add blocks and catastrophically expensive to change old ones. Miners are rewarded with a block reward for their effort, giving them a strong financial reason to play by the rules rather than try to cheat.
Together, these properties create something that did not exist before Bitcoin: a digital record that is permanent, public, and trustworthy — without needing to trust anyone in particular.
As of early 2026, the Bitcoin blockchain has grown to over 700 gigabytes of data, recording every transaction since the network launched on January 3, 2009. It has operated continuously since that day without a single minute of downtime.
What’s Next
The blockchain is the backbone of Bitcoin — the technology that makes trustless digital money possible. To understand how the blockchain stays secure, read about proof of work. To see how the blockchain was first described, explore The Bitcoin Whitepaper Explained. And for the big picture of what Bitcoin is and why it exists, start with What is Bitcoin?.