Field guide to bitcoin
Bitcoin, read plainly.
Halvern explains what bitcoin is, how its ledger stays consistent, how new coins are issued, and where people get hurt. The language is ordinary. The hype stays out.
The short version
A record no one owns and anyone can check.
Bitcoin is a shared ledger of who controls which coins. Transfers are gathered into batches, and a batch is accepted only when independent node operators confirm that it follows the published rules.
Nothing here asks you to trust a company. The rules are public, the software that enforces them is public, and anyone can run a copy to check the record. The price of that independence is that no office exists to reverse a payment or restore a lost key.
Blocks and history
Each block points back at the one before it.
A block bundles recent transfers and carries a fingerprint, called a hash, of the block before it. If anyone edits an old transfer, its fingerprint changes, and every later block stops matching. To hide an edit, someone would have to redo the work for that block and every block after it, faster than the rest of the network adds new ones.
Change a transfer in Block 1 and its fingerprint changes. Block 2 still holds the old one, so the link breaks.
Issuance
The schedule is written into the rules.
New coins enter circulation as the reward for adding each block. The reward starts at 50 coins and halves every 210,000 blocks, which is about four years at the target pace of one block every ten minutes.
Because each cut is a fixed fraction of the one before, the reward series adds up to just under 21 million coins and never exceeds that figure. Since the fourth halving in April 2024, the reward has been 3.125 coins per block.
Keys and ownership
Ownership is a signature, not a login.
A private key is a long secret number that can produce signatures. From it come a public key and an address, which you can share with anyone who wants to pay you.
To spend coins, the owner signs a transfer with the private key, and every node checks that signature against the public key. Whoever holds the private key controls the coins. That is why the key must stay secret, and why losing it means losing the ability to sign.
Next step
Start with the principles.
Bitcoin's design rests on principles that pull against each other: fixed supply, self-custody, final settlement and more. The ranking exercise asks you to place them in an order. Nothing is scored, and no order is the correct one.
How we write: we describe mechanisms and their trade-offs. We do not forecast prices, recommend purchases, or print figures that change from day to day. A number on this site is either a fixed protocol rule or a well-known definition.