Glossary

Block

Plain-language definition Crypto glossary

Key takeaways

A block is a batch of transactions bundled together and added to a blockchain as one unit, acting like the pages of the ledger added in sequence to form the chain.
Each block contains validated transactions, a timestamp, and a cryptographic reference to the previous block, which chains them in order, with the consensus mechanism deciding who adds the next block.
Grouping transactions into linked blocks is what gives a blockchain its tamper-resistant order, while a block's size and how often blocks are produced shape a network's capacity and fees.

Definition

A block is a batch of transactions bundled together and added to a blockchain as one unit. Blocks are the “pages” of the ledger, added in sequence and linked to form the chain.

How it works

Each block contains a set of validated transactions, a timestamp, and a cryptographic reference to the previous block, which is what chains them in order. The network’s consensus mechanism decides who gets to add the next block; on a proof-of-work chain that is the winning miner, who also receives the block reward. Once added and confirmed by later blocks, a block’s contents become very hard to change.

Why it matters

Grouping transactions into linked blocks is what gives a blockchain its tamper-resistant order. A block’s size and how often blocks are produced also shape a network’s capacity and fees.

Example

The very first block of a blockchain is called the genesis block, the foundation every later block builds on.

FAQ

Frequently asked questions

How are blocks linked together in a blockchain?

Each block contains a cryptographic reference to the previous block, which chains them in order. This linking means that altering one block would break its connection to the others, making confirmed history very hard to change. The result is a tamper-resistant, sequential ledger.

Who decides what goes into a block?

The network's consensus mechanism decides who gets to add the next block. On a proof-of-work chain that is the winning miner, who also receives the block reward, while proof-of-stake chains use a chosen validator. The block producer selects validated transactions to include, subject to the block's size limits.

What is the genesis block?

The genesis block is the very first block of a blockchain, the foundation that every later block builds on. Because it is the starting point, it has no previous block to reference. All subsequent blocks are linked back, directly or indirectly, to this original block.