How Does Bitcoin Work?

How Bitcoin Transactions and the Blockchain Work

When you send bitcoin to another person, you broadcast a signed transaction to the Bitcoin network. Your digital signature — produced using your private key — proves ownership without revealing the key itself. Network participants called nodes verify the signature and confirm you haven't already spent those funds (preventing double-spending). Valid unconfirmed transactions collect in a waiting area called the mempool until a miner picks them up and includes them in a block.

Miners compete to add the next block to the blockchain by repeatedly hashing block data until they find an output that satisfies the network's current difficulty target — a number that starts with a required number of leading zeros. This process, called proof of work, requires enormous computational effort and is deliberately hard to do but trivially easy for the rest of the network to verify. The winning miner broadcasts the completed block; every other node independently checks it, and if valid, appends it to their own copy of the blockchain. The miner receives newly issued bitcoin (the block reward) plus any transaction fees included in the block.

A common misconception is that bitcoin exists as a file or coin on your device. In reality, bitcoin balances are entries in the blockchain ledger — your wallet software simply holds the private keys that authorize you to spend those entries. There is no central server keeping track of balances; every full node in the network maintains an independent copy of the complete transaction history and arrives at the same account balances by replaying every transaction from the genesis block forward.

Key Points

• Bitcoin uses a peer-to-peer network — there is no bank, company, or government controlling it. Rules are enforced by software run by tens of thousands of independent nodes.
• Proof-of-work mining secures the network by making it computationally expensive to rewrite transaction history. An attacker would need to outpace the combined hash rate of all honest miners.
• Bitcoin's supply is hard-capped at 21 million coins. The block reward halves roughly every four years, slowing the rate of new issuance over time.
• Transactions are irreversible once confirmed. A transaction buried under several blocks is considered effectively permanent because rewriting it would require redoing all subsequent proof-of-work.

Learn More

Understanding Bitcoin is the foundation for understanding the broader cryptocurrency ecosystem — blockchains, smart contracts, DeFi, and token economics all build on the same core concepts. See Crypto Fundamentals for a complete walkthrough of how cryptocurrencies work, how to evaluate them, and how to manage risk.

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Related Questions

What is Bitcoin mining?

Bitcoin mining is the process by which new transactions are verified and added to the blockchain. Miners compete to solve a computationally intensive cryptographic puzzle — finding a hash that meets the network's current difficulty target. The first miner to find a valid solution broadcasts the new block to the network, earns the block reward (newly issued bitcoin), and collects transaction fees from all transactions included in that block.

How many bitcoins will ever exist?

Bitcoin's protocol caps the total supply at 21 million coins. This limit is enforced by code: the block reward paid to miners is halved approximately every four years in an event called the halving, progressively reducing the rate of new issuance. The last bitcoin is projected to be mined around the year 2140, after which miners will be compensated solely by transaction fees.