ShopA beginner's explanation of what Bitcoin is and how it works
Bitcoin is a peer-to-peer electronic cash system.
It was first announced on October 31, 2008, in the form of a nine-page technical document known as the Bitcoin whitepaper. The whitepaper was written by a person or group going by the name of Satoshi Nakamoto and it outlined how Bitcoin works: how transactions are made, how ownership is established, and how the system operates without any central authority.
Bitcoin launched on January 3, 2009, and has operated continuously ever since.
What Problem Does Bitcoin Solve?
Bitcoin solves two key challenges:
- It enables electronic cash transfers directly between people, anywhere in the world, without a bank in the middle.
- It operates with a fixed supply limit of 21 million, which is not subject to any authority's decision.
Those two properties, electronic peer-to-peer transactions and a fixed supply limit, are what make Bitcoin different from everything that came before it. To understand the significance, it is useful to understand what exactly peer-to-peer electronic cash means.
Peer-to-Peer Electronic Cash
Physical cash is peer-to-peer. When you hand someone a $20 bill, the transaction is direct, immediate, and final. No bank needs to approve it and no institution holds the money on your behalf. The money changes hands and the exchange is complete.
Electronic cash is not peer-to-peer. When you pay someone $20 through a bank transfer or payment app, your bank updates a record in its database and the recipient's bank updates a record in theirs. What actually happens is a coordinated update to digital records, maintained by the banks. Electronic payments have always required third party involvement, to both custody funds and facilitate transactions. Those institutions can freeze accounts, reverse transactions, or refuse service entirely.
Bitcoin is the first cash system that is both electronic and peer-to-peer.
A transaction between two holders of bitcoin (lowercase "b" for the asset) does not require any institution to approve, custody, or record it. It is broadcast to a global network of peers, confirmed according to established rules, and settled without relying on any third party.
Fixed Supply Limit
Physical cash, for all its peer-to-peer properties, is still subject to central bank policy. The central bank of a given country can print more of it, which dilutes the value of all money already in circulation. Electronic money has the same vulnerability, where expanding the money supply is as easy as typing numbers into a computer.
Bitcoin removes this monetary inflation problem entirely. Its supply schedule, with a terminal limit of 21 million, is encoded in the software and enforced by every participant in the network. No authority can "print" bitcoin.
Together, these properties mean Bitcoin removes the dependency on third parties that traditional money requires: the commercial banks that serve as gatekeepers for transactions and custody, and the central banks that can decrease the money's value through inflating the supply.
How Does Bitcoin Track Ownership?
Bitcoin operates as a distributed public ledger, maintained by countless computers running the Bitcoin software, called "nodes". Ownership of bitcoin exists in the ability to authorize a transaction, or "spend" bitcoin from a particular address, which can only be done by the holder of the unique private key associated with the address.
Unlike banks, where accounts are debited and credited on a centrally controlled ledger, the nodes in Bitcoin's network hold their own copies of the ledger, meaning no "master copy" exists. Individual nodes can be shut down, seized, or destroyed without affecting the network as a whole. The system remains operational so long as a single node continues to run the Bitcoin software, which is free, open-source, and can be run on any standard computer.
Running your own node means more than storing a copy of the ledger. Encoded in Bitcoin's software are the rules that govern how Bitcoin operates, including how nodes are to connect, how transactions are to be formatted, and what constitutes a valid or invalid transaction. Two of the most important rules:
- Valid Signature. Every transaction must include a valid digital signature, created from the private key associated with the bitcoin being spent.
- Supply Schedule. No transaction can create bitcoin outside the pre-programmed supply schedule, with its terminal limit of 21 million.
In this way, nodes are the rule-enforcers that ensure every transaction and every group of transactions (known as "blocks"), obey the rules.
Ultimately, ownership comes down to this: On Bitcoin's ledger is a record of an amount of bitcoin sent to an address to which you control the private key. That amount can only be spent by authorizing a transaction with a digital signature, requiring that private key. If you hold that private key, you control that bitcoin. If someone else holds the private key, they control it.
This is why bitcoiners use the phrase "Not your keys, not your coins." What are private keys and public keys?
How Does Bitcoin Confirm Transactions Without a Bank?
The innovation described in the Bitcoin whitepaper is how to get countless independent parties to agree on a single version of the ledger, with no central authority in charge. The mechanism Bitcoin uses is called "proof of work", and the process of participating in it is called "mining".
With a distributed public ledger, there is no obvious way to resolve conflicting versions of the ledger. Bitcoin's solution is an open lottery-style competition called mining, where anyone can participate and the winner earns the right to add the next block of transactions to the ledger and get paid a reward for doing so.
How Does Bitcoin Mining Work?
The entire process of works as follows:
- Initiating. A bitcoin holder creates a transaction, signs it with their digital signature, and broadcasts it to the network. Nodes validate that the transaction follows the rules and add it to their own pool of transactions in waiting, called a "mempool."
- Building. Computers participating in the competition, called "miners", select transactions from the mempool and assemble them into a candidate block that has strictly limited capacity.
- Mining. To "win the lottery", the miner must find a number that, when combined with the block's contents, produces a result meeting precise target criteria set by the network. There is no way to find a valid number in advance, so miners must use trial-and-error to guess a number until one works. This is the "work" in proof of work, and it consumes real resources like energy.
- Broadcasting. When a miner finds a winning number, they broadcast their proposed block to the network.
- Validating. Every node independently verifies that the number meets the target criteria and that the block and all its transactions follow the rules.
- Rewarding. If the block passes validation, nodes add it to their copy of the ledger and the miner receives the reward: the "block subsidy" of newly issued bitcoin plus transaction fees paid by people transacting.
- Repeating. The new block serves as an input for the next round of competition. Miners immediately begin competing to add the next block, in a never-ending process of mining.
- Difficulty Adjusting. Every 2,016 blocks, the Bitcoin software automatically adjusts the target to maintain ten minute block intervals. If miners collectively deploy more computational power, accelerating their rate of guessing and block production, the difficulty rises to make finding a winning number harder. Conversely, if mining power decreases, the difficulty drops, ensuring blocks occur on average every ~10 minutes regardless of global deployed power.
Notably, each block contains a cryptographic summary fingerprint of the block before it, which itself contains a fingerprint of the block before that, forming an unbroken chain of blocks ("blockchain") back to the very first block. This structure makes the ledger tamper-evident, as any alteration would change that block's fingerprint, breaking its link to every block that followed.
This system is intentionally asymmetric. Mining a block is difficult and expensive, whereas verifying that a block is valid is cheap and easy. If a block contains a single invalid transaction, every node on the network rejects it immediately and the miner's efforts are wasted. The result is that everyone in the network is strongly incentivized to play by the rules.
What Is Bitcoin Mining?
Mining is how Bitcoin operates as a peer-to-peer electronic cash system, where transactions are added to the ledger with no central authority.
The term "proof of work" is used because the only known way to generate the winning number is by trial and error, requiring computer hardware and electricity. Having a winning number is proof that work was performed.
Bitcoin mining serves multiple purposes simultaneously:
- Issuing new bitcoin. The block subsidy is the only way new bitcoin can be issued into circulation, and the amount of new bitcoin must follow the pre-programmed supply schedule.
- Confirming transactions. Mining is what moves transactions from "pending" in the mempool into confirmed on the ledger.
- Chronological conflict resolution. Mining establishes a definitive, time-ordered sequence of transactions. Conflicting versions of the blockchain are resolved as the version with the most proof of work behind it is the winner.
- Prioritizing transactions. Miners are incentivized to include transactions in the blocks through transaction fees, typically selecting the highest-paying entries. This creates a competitive free market, where users bid for faster confirmations.
- Hardening immutability. Each new block adds a layer of security to the entire transaction history. Altering a previous transaction requires re-mining every block produced since that transaction and outpacing the network's cumulative proof of work.
- Securing the network. The computational resources required to produce blocks makes it prohibitively expensive for any party to block, reverse, or monopolize the chain. The cost of attacks grows as miners deploy more computational power.
What Is Bitcoin's 21 Million Supply Limit?
One of the key rules encoded in Bitcoin's software is the supply schedule, which started at zero and is progressing toward a terminal limit of 21 million. Every node enforces this schedule independently, checking every transaction and block against it. All participants are incentivized to keep this rule and heavily discouraged from change it.
New bitcoin enters circulation exclusively through the block subsidy paid to miners. When Bitcoin launched in 2009, each block's subsidy was set at 50 bitcoin. Every 210,000 blocks, roughly four years, that reward is automatically cut in half in an event called a "halving". This supply schedule of ~4 year halvings continues until the reward diminishes to zero, sometime in the year 2140. At that point the 21 million limit is reached and no new bitcoin are issued.
Every node independently validates that each block's subsidy does not exceed the scheduled allotment. If a miner produces a block with more than the allowed amount, every node instantly rejects the block. Since mining is expensive and detecting and rejecting invalid blocks costs nodes essentially nothing, miners are strongly incentivized to follow the supply schedule.
Nodes themselves are also incentivized to keep to the supply schedule. Bitcoin's value as a cash system is connected to its scarcity and predictable supply. Every node operator, miner, and bitcoin holder has a direct financial interest in keeping the 21 million limit intact. Changing the limit would require convincing the nodes to voluntarily download a new version of the Bitcoin software that undermines the value of their assets.
The supply limit is not just technically enforced, it is economically defended by all participants acting in their own self-interest.
Who Controls Bitcoin?
No one controls Bitcoin. There is no headquarters, no governing body, no CEO, and no single server. Bitcoin is a distributed ledger, managed by a decentralized network of independent peers, running free and open-source software, and each participant in the network is redundant.
Each full node holds a complete copy of the ledger and each enforces Bitcoin's rules independently. Individual nodes can be removed or added to the network without affecting the network as a whole.
The software itself is publicly available and fully auditable. Anyone can read it, inspect it, copy it, or modify it. But what they cannot do is force anyone else to download and run their modified version.
If you modify your copy of Bitcoin's rules and broadcast transactions based on your altered version, every other node on the network will reject any transactions that are incompatible with their rules. While it is trivially easy to modify your version of Bitcoin, it is difficult to impossible to get the network as a whole to opt-in and adopt your rule changes. If a rule change is detrimental to the operations of the network or the value of bitcoin, it will be rejected.
With Bitcoin, there is no authority to appeal to and no mechanism to force other node operators to run a specific version of Bitcoin's software. Bitcoin's rules are durable because they are established by consensus, not by force.
Governments cannot ban Bitcoin itself, they can only ban or regulate their citizens from interacting with Bitcoin within their borders. Bitcoin operates as a global network of redundant, self-interested actors running open-source software on standard hardware. Miners are also redundant and effectively mobile, as they can simply relocate their operations to new jurisdictions.
What Does This Actually Mean for You?
Bitcoin's peer-to-peer properties and fixed supply limit have practical implications. Unlike legacy digital money that exists as records held inside banks' databases and can be inflated through printing by central banks, bitcoin can be held, verified, and transacted without any third party involved. It is the first true peer-to-peer electronic cash system.
"Holding" bitcoin means different things depending on the arrangement. Three common options exist, but they are not equivalent:
- A bitcoin ETF. An ETF gives you financial exposure to bitcoin's price movements, but does not give you any ownership of bitcoin. The ETF typically holds bitcoin through a third-party custodian that controls the private keys, and there are no options to withdraw bitcoin to your own custody.
- Exchange custody. This arrangement functions like a bank deposit where the exchange holds the private keys and you hold a claim against them. If the exchange fails, freezes withdrawals, or is compelled to block your account, you have no recourse.
- Self-custody. Self-custody is true ownership of bitcoin. You have exclusive control over your private keys, ensuring no one can freeze or confiscate your funds. You remain fully sovereign, able to hold, verify and spend your bitcoin without relying on any third party.
Bitcoin is a peer-to-peer electronic cash system, and that property only exists for you if you control the keys that authorize your transactions.
Related articles
How does a Bitcoin transaction work?
How bitcoin moves from one address to another, and what happens between broadcast and confirmation
What is a Bitcoin wallet?
what a wallet actually is, how it manages keys, and the difference between custodial and self-custodial options
What gives Bitcoin value?
The monetary properties that underpin Bitcoin's role as a savings instrument