What is a blockchain?

Written and maintained by the BTCNATOR editorial team • Last updated September 8, 2026 • How we research

Quick answer

A blockchain is a shared digital ledger that many computers keep an identical copy of. New records are added in batches called blocks, and each block is cryptographically linked to the one before it. Because thousands of independent participants would all have to agree to change a past block, records that are already several blocks deep are treated as permanent.

Detailed explanation

Traditional databases are held and edited by one organisation. A blockchain removes that single point of control: the same ledger is replicated across a network of nodes, and a defined consensus process decides which new block everyone accepts next.

Each block contains a list of transactions, a timestamp, and a hash — a short fingerprint — of the previous block. Changing any past transaction would change that block’s hash, which would break the link to every block after it. Redoing all of that work faster than the rest of the network is generally infeasible on a large chain.

Blockchains can be public (anyone can read, transact and run a node, e.g. Bitcoin and Ethereum) or permissioned (a known set of organisations, used by some enterprises).

How it works

Submit. A user signs a transaction and broadcasts it to the network.
Validate. Nodes check that it follows the rules (valid signature, funds not already spent).
Order. A block producer — a miner (proof of work) or a validator (proof of stake) — selects transactions and proposes the next block.
Agree. The network’s consensus rules determine whether that block is accepted and built upon.
Confirm. Once included, the transaction has one confirmation; each subsequent block adds another and increases finality.

Why records cannot simply be edited

There is no "edit" or "delete" operation. The only way to correct something is to publish a new transaction. This is a deliberate design choice: it is what lets strangers trust the ledger without trusting each other. It also means mistakes are costly — a wrong address or wrong network cannot be undone by an administrator.

Key facts

A block links to the previous block by its hash, forming a chain.
Public blockchains are validated by proof of work (mining) or proof of stake (validators).
"Finality" means how confident you can be that a block will never be reversed; it grows with each confirmation.
The ledger is transparent: anyone can inspect every transaction with a block explorer.
No central administrator can reverse, redirect or freeze an ordinary confirmed transaction on a public chain.

Risks and limitations

Irreversibility cuts both ways: errors and theft are usually permanent.
Small or new blockchains can be more vulnerable to having recent blocks reorganised.
Smart contracts recorded on a blockchain can still contain bugs; the chain guarantees the code ran, not that the code is correct.
"Blockchain" in a product name does not by itself mean the product is safe, audited or decentralised.

FAQ

Is a blockchain the same as Bitcoin?

No. Bitcoin is one blockchain. Many others exist (Ethereum, and hundreds more), each with its own rules, and some blockchains are private to a group of companies.

What is a confirmation?

A confirmation means your transaction is in a block. Each additional block mined on top adds another confirmation and makes reversal exponentially less likely.

Can data on a blockchain be deleted?

Not in the normal sense. The ledger is append-only. Corrections are made by adding new transactions, not by editing old ones.

Is everything on a public blockchain visible?

Yes. Transaction amounts, addresses and timestamps are public. Addresses are pseudonymous rather than anonymous.