What is a Block?
A collection of Bitcoin transactions that are grouped together and added to the blockchain. A new block is created approximately every 10 minutes. Each block contains a cryptographic reference to the previous block, creating an unbreakable chain of transaction history.
Why It Matters
Blocks are the fundamental building blocks of Bitcoin's security and record-keeping system. By grouping transactions into blocks and linking them with cryptography, Bitcoin creates a tamper-proof ledger. If someone tries to alter a past transaction, it would change that block's cryptographic hash, which would break the link to all subsequent blocks. This makes Bitcoin's history impossible to rewrite without redoing the enormous computational work from every block onward. Blocks also limit how many transactions can be processed in a given time, which is why understanding blocks helps you grasp Bitcoin's scalability challenges and why fees matter.
How It Works
Miners collect pending transactions from the mempool and bundle them into a new block. Each block contains a block header with metadata including the previous block's hash (linking the chain together), a timestamp, the mining difficulty target, and a special number called a nonce. Miners then compete to find a valid nonce that produces a hash meeting the difficulty requirement—this is where the computational work of Proof of Work happens. Once a miner finds a valid solution, they broadcast the new block to the network. Other nodes verify the transactions in the block and add it to their copy of the blockchain.