What is a Blockchain?
The public ledger that records every Bitcoin transaction ever made. It's called a blockchain because transactions are grouped into blocks, which are then linked together in chronological order. Once added to the blockchain, transactions cannot be altered or deleted.
Why It Matters
The blockchain is the innovation that makes Bitcoin work without requiring trust in a central authority. Instead of relying on a bank to keep accurate records, thousands of independent computers maintain identical copies of the blockchain. This transparency means anyone can verify the entire history of bitcoin—you don't have to trust Coinbase, your government, or anyone else. The blockchain's immutability also prevents double-spending, the fundamental problem Bitcoin solved. Once a transaction is buried under several blocks, it's mathematically impractical to change it, giving you certainty that your payment was final.
How It Works
The blockchain starts with the Genesis Block and grows chronologically as new blocks are added approximately every 10 minutes. Each block references the previous block's hash, creating a cryptographic chain. This design means altering any old transaction would require not only changing that block but recalculating the hash for every block that came after it. Full nodes download and validate the entire blockchain from the beginning, verifying that every transaction follows Bitcoin's rules and that coins aren't spent twice. This is why the blockchain's complete history is accessible to anyone with the storage space—it's the ultimate audit trail.