What is Blockchain?

A blockchain is a type of distributed database where data is organized into blocks that are cryptographically linked together in chronological order, forming a chain. Once a block is added to the chain, the data it contains is extremely difficult to alter without invalidating every subsequent block — which is what gives blockchains their characteristic immutability.

How a blockchain works

1. Transactions are broadcast to a peer-to-peer network of nodes.
2. Nodes validate the transactions against the network’s consensus rules.
3. Validated transactions are bundled into a new block by block producers (miners in proof-of-work systems, validators in proof-of-stake systems).
4. The new block is added to the chain, and the updated ledger is propagated to all nodes.

Because every node holds a copy of the same ledger, there is no single point of failure and no central authority that can rewrite history. This is the core innovation that allows cryptocurrencies to function without banks.

Public vs. private blockchains

Most cryptocurrencies — including Bitcoin, Ethereum, Solana, and the networks you see in our chains directory — run on public blockchains that anyone can read, write to, and participate in securing. A smaller set of enterprise use cases use private blockchains with restricted participation, though these are generally not used for payments.

Block time and finality

Different blockchains produce blocks at different rates. Bitcoin produces a block roughly every 10 minutes; Ethereum produces one roughly every 12 seconds. “Finality” — the point at which a transaction is considered irreversible — varies by chain and consensus mechanism. For merchants accepting crypto, finality matters because it determines how quickly you can consider a payment settled.