Why Bitcoin exists and how it works
Build from money itself to hashes, keys, transactions, mining, consensus, and a live payment journey.
Key qualities of Bitcoin
Structure and control
- No issuer. No central bank or government creates it. New coins come only from mining, by fixed rules.
- No company. No corporation, CEO, headquarters or shareholders own it.
- No leader. Its creator, Satoshi Nakamoto, is anonymous and has not been heard from since about 2011.
- Decentralized. Thousands of independent nodes worldwide keep and check copies of the ledger.
- Permissionless. The protocol lets anyone use it, mine it or run a node without approval, though some countries restrict mining or exchanges.
- Open source. The code is public, and anyone can audit it or propose changes.
- Changes need broad agreement. Rule changes only stick if node operators adopt them, so it is hard for any group to force them.
Monetary properties
- Fixed supply. Nodes reject any block that pays its miner more new coins than the halving schedule allows, so the total can never pass 21 million BTC.
- Predictable issuance. New supply halves every 210,000 blocks, roughly every four years (the halving), on a known schedule.
- Divisible. One BTC splits into 100 million satoshis.
- Fungible. Units are mostly interchangeable, though a coin’s public history can follow it.
- No inflation by decree. Nobody can print more to fund spending.
Transactions
- Peer-to-peer. Value moves directly between users with no bank in between.
- Borderless. The protocol works the same in every country with internet access, though access to exchanges varies.
- Final in practice. There are no chargebacks, and each new block on top makes reversing a payment much harder.
- Censorship-resistant. It is hard for any party to block a valid transaction.
- Always open. The network runs 24 hours a day, with no business hours or holidays.
Security and trust
- Verifiable. You can check the whole history yourself instead of trusting an institution.
- Proof of work. Mining ties security to real-world energy and computing cost.
- Hard to rewrite. Changing past blocks means redoing their work, which is extremely costly.
- Transparent. Every on-chain transaction is publicly visible on the blockchain.
- Pseudonymous. Addresses are not tied to names by default, though analysis can often link them.
Ownership
- Self-custody. Whoever holds the private keys controls the coins (“not your keys, not your coins”).
- Bearer asset. Like cash, whoever controls the keys controls the coins, and anyone with a copy of a single-signature key can spend them.
- Seizure-resistant. Keys can be memorized or hidden, which makes them hard to confiscate, though the holder can still be pressured to hand them over.
- No recovery. Lose your keys and the coins are gone for good, with no help desk.
Watch a payment cross the world
Follow Alice's payment as it is signed, checked by nodes, relayed through the mempool, mined, and confirmed.
Lessons
10 short lessons, in order. Each ends with a quiz.
Why Bitcoin?
Who controls the money ledger, and what happens to you when they say no?
10 min lessonUSD vs Gold vs Bitcoin
Different money systems make different tradeoffs in scarcity, portability, verification, and censorship resistance.
6 min lessonHashes: Digital Fingerprints
A cryptographic hash is a one-way function that makes tampering visible and proof of work possible.
5 min with widgetKeys and Signatures
You do not have an account. You have a mathematical key that authorizes spending.
5 min with widgetAddresses and Spending Conditions
An address is a spending condition, not an account.
5 min with widgetTransactions, Change and Fees
Bitcoin transactions do not subtract from a balance; they consume old outputs and create new ones.
8 min lessonNodes: The Rule Checkers
Nodes give Bitcoin users power by independently rejecting invalid transactions and blocks.
6 min lessonMining: The Global Lottery
Miners spend real energy to propose blocks and earn the subsidy plus fees.
8 min with widgetConsensus and Reorganizations
Consensus is how independent participants converge on one valid history without a leader.
5 min lessonPayment Journey
Follow a payment from wallet intent to confirmed settlement.
6 min lessonBitcoin’s issuance, over time
New BTC per year at one block every ten minutes. Linear bars share a zero baseline. Actual calendar-year totals depend on block timing; 2028 is an approximate future halving date.
This is an issuance schedule, not a Bitcoin price forecast or a comparison of investment returns. The supply cap does not prevent a fall in purchasing power.
Put the whole payment journey together
Try without looking back. Check your answers, then revisit any explanation you missed. These practice checks do not certify readiness to handle real funds.