Bitcoin Fundamentals

05 September 2026

Bitcoin is a decentralized digital currency that operates without a central authority. It enables peer-to-peer value transfer over the internet using a combination of cryptography, consensus mechanisms, and economic incentives. This page surveys how Bitcoin works at the protocol level, the tools people use to interact with it, the decisions they face, and the risks involved. Each section introduces a topic and points to a dedicated page that answers the specific question in full.

How bitcoin creates and confirms transactions

Bitcoin does not track account balances. Instead, it uses a system of unspent transaction outputs (UTXOs). Every transaction consumes existing UTXOs as inputs and creates new UTXOs as outputs. Your "balance" is simply the sum of all UTXOs your private keys can control. The page [How does the Bitcoin UTXO model work for beginners] explains this model in detail, including why it prevents double-spending and how change outputs work.

A Bitcoin transaction begins its life off-chain. You create it in a wallet, sign it with your private key, and broadcast it to the network. The transaction enters every node's mempool - a temporary holding area for unconfirmed transactions. Miners select transactions from the mempool, prioritizing those with higher fee rates. Once a miner includes your transaction in a block, it receives its first confirmation. Each subsequent block built on top adds another confirmation. The page [What is the lifecycle of a Bitcoin transaction from creation to confirmation] walks through every stage from signing to final settlement.

Transaction fees serve two purposes: they compensate miners for securing the network and they allocate scarce block space to the most valuable transactions. Fees are denominated in satoshis per virtual byte (sat/vB). When the mempool is full, users compete in an auction, and fees rise. When the mempool is empty, the lowest possible fee is the minimum relay fee, typically 1 sat/vB. The page [How do Bitcoin transaction fees work and why do they matter] explains the fee market mechanics and how to estimate appropriate fees.

The Engine: Proof of Work and Mining

Bitcoin's security comes from proof-of-work consensus. Miners compete to find a block hash that is below a target value. They do this by varying a small field in the block header called the nonce and hashing repeatedly. There is no shortcut; the only way to find a valid hash is brute force. The first miner to succeed broadcasts the block to the network. Other nodes verify it and extend their chain. The page [How does proof of work work in Bitcoin mining] covers what the "work" actually is, why it costs energy, and how it makes rewriting history prohibitively expensive.

The difficulty of finding a valid hash adjusts automatically. Every 2,016 blocks - roughly two weeks - every node recalculates the target so that the average time between blocks stays near 10 minutes. If miners join and blocks come faster than 10 minutes, difficulty increases. If miners leave and blocks slow down, difficulty decreases. This mechanism keeps the issuance rate predictable regardless of total hash rate. The page [How does Bitcoin mining difficulty adjustment work] explains the math and the implications for miners and users.

The block reward is the incentive for miners. It consists of two parts: the coinbase transaction, which creates new bitcoin out of nothing, and the sum of all transaction fees in the block. Every 210,000 blocks (approximately four years), the coinbase subsidy is cut in half. This event is called the halving. As the subsidy declines over time, transaction fees are expected to become the primary miner reward. The coinbase output cannot be spent until 100 more blocks have been mined - a rule called coinbase maturity.

A block is not just a list of transactions. It has a specific structure: a header containing the previous block's hash, a timestamp, the difficulty target, a nonce, and a Merkle root - a single hash that commits to every transaction in the block. Changing any transaction changes the Merkle root, which changes the block hash, which breaks the link to the next block. The page [What is inside a Bitcoin block structure and how are blocks linked] examines every field in the header and how the Merkle tree works.

The cryptography that controls your bitcoin

Owning bitcoin means controlling the private key for an address. Bitcoin uses the secp256k1 elliptic curve and the ECDSA signature algorithm. A private key is a random 256-bit number. From it, you derive a public key, which you can safely share. To spend bitcoin, you produce a digital signature that proves you know the private key without revealing it. The page [How does Bitcoin use public key cryptography to secure funds] explains the mathematical relationship between keys and how signatures work.

An address is not a public key. It is a hash of the public key, processed through SHA-256 and then RIPEMD-160, with a version byte and a checksum appended. This means the public key is not revealed until you spend from the address, adding a layer of security against quantum attacks. The page [How is a Bitcoin address generated from a public key] shows the exact steps, from public key to the Base58Check string you share.

Modern wallets do not store a single private key. They use hierarchical deterministic (HD) wallets as specified in BIP32. A single seed phrase - typically 12 or 24 words from the BIP39 word list - derives an entire tree of keypairs. One master seed generates millions of addresses without ever needing to back up individual keys. The page [How do HD wallets work with a Bitcoin seed phrase] covers how the derivation works, what BIP32 paths are, and why a passphrase adds plausible deniability.

There are several address formats. Legacy (P2PKH) starts with 1. SegWit (P2WPKH) starts with bc1q and reduces fees by separating witness data. Taproot (P2TR) starts with bc1p and enables Schnorr signatures and more complex scripts. Each format has different trade-offs in fee cost, feature support, and compatibility. The decision between legacy, SegWit, and Taproot affects transaction fees and what you can do with your bitcoin.

Tools of the Trade

Bitcoin Core is the reference implementation and the backbone of the network. It validates every transaction and block according to consensus rules. Running a full node gives you the highest level of security: you do not trust anyone else to tell you what the blockchain contains. The page [Bitcoin full node vs light client what is the difference] compares the trust models and resource requirements.

For users who do not want to run a full node, light clients like Electrum connect to servers that provide filtered blockchain data. Electrum servers such as Fulcrum and Electrs index the blockchain for fast queries. Light clients are convenient but trust the server to provide correct data. The page [Bitcoin full node vs light client what is the difference] explains the trade-offs.

Hardware wallets - Ledger, Trezor, Coldcard, BitBox02, Blockstream Jade, SeedSigner - store private keys on a dedicated device that never exposes them to the internet. They sign transactions offline and transmit only the signature to your computer or phone. The page [Hardware wallet vs software wallet for Bitcoin which is safer] explains why hardware wallets protect against malware and clipboard attacks.

Software wallets like Sparrow Wallet, BlueWallet, and Electrum run on general-purpose devices. They are convenient for daily spending but vulnerable to malware, keyloggers, and screen capture. The page [What is the difference between a hot wallet and cold storage for Bitcoin] helps you decide which to use for spending versus saving.

Multisignature wallets require M-of-N signatures to spend. A 2-of-3 multisig, for example, needs two out of three private keys to authorize a transaction. This distributes risk: losing one key does not mean losing your bitcoin. The page [How does multisignature work for Bitcoin security] covers how multisig addresses work, the script behind them, and the coordination tools like Specter Desktop and Nunchuk.

The second layer: lightning network

On-chain Bitcoin settles every transaction permanently, but it processes only about seven transactions per second. For small, frequent payments, that is impractical. The Lightning Network addresses this by creating payment channels between participants. You open a channel with an on-chain transaction, then send unlimited payments back and forth with your channel partner - only the opening and closing transactions touch the blockchain.

Lightning requires managing liquidity. You can only receive what others can send to you (inbound liquidity) and only send what you have in your channels (outbound liquidity). The page [Bitcoin Lightning Network vs on-chain payments what is the difference] explains when to use each layer.

Lightning implementations include LND, Core Lightning, and Eclair. Wallets like Phoenix, Breez, and Zeus connect to your own node or to a third-party service. Running your own Lightning node gives you full control but requires uptime and channel management. Using a custodial Lightning wallet is simpler but means trusting the provider not to lose or steal your funds. Tools like Umbrel and Start9 Embassy simplify running a Bitcoin and Lightning node at home.

Critical decisions and common risks

Self-custody versus exchange custody is the most consequential decision a Bitcoin user makes. Self-custody means you control the private keys. You are responsible for backup, security, and inheritance. An exchange holds the keys for you, but your bitcoin is an unsecured liability on the exchange's balance sheet. When exchanges like Mt. Gox, QuadrigaCX, and FTX failed, customers became creditors in bankruptcy proceedings. The page [Should I hold bitcoin in self custody or on an exchange] examines the trade-offs in detail. The page [What happens to your bitcoin if an exchange goes bankrupt] explains the legal reality.

Seed phrase loss is irreversible. There is no "reset password" for bitcoin. If you lose your seed phrase, you lose access to your funds permanently. The page [How to protect your Bitcoin seed phrase from loss and theft] covers backup methods - metal stamping, multiple locations, passphrase defenses - and what not to do.

Seed phrase theft is equally permanent. Scammers use phishing websites that ask you to "verify your wallet" by entering your seed phrase. Fake wallet apps on app stores steal keys from the moment you create a wallet. The page [How to avoid Bitcoin seed phrase phishing scams and fake wallets] lists the most common attack vectors and how to recognize them.

Address reuse harms privacy. When you reuse an address, anyone can see all payments to and from that address belong to the same entity. Using a new address for every transaction - which HD wallets do automatically - is the standard practice for privacy.

Fee underpayment can leave a transaction stuck in the mempool indefinitely. If you did not signal replace-by-fee (RBF), you cannot bump the fee. If you have no change output, you cannot use child-pays-for-parent (CPFP). Understanding these mechanisms before you send a transaction prevents frustration.

Lightning channel force-closes happen when your channel peer goes offline or cheats. The channel closes unilaterally, and the funds are locked for a timelock - usually 144 blocks (about 24 hours) for small channels, up to 2,016 blocks (two weeks) for large ones. During this time, you cannot spend the funds, and you pay on-chain fees for the close transaction.

How the pieces fit together

Bitcoin is a system of interdependent parts. Proof of work secures the chain. The UTXO model tracks ownership. Cryptography enables trustless control. Mining difficulty stabilizes issuance. Transaction fees allocate scarce block space. Hardware wallets protect keys. Lightning scales micropayments. Each component exists because the others alone are insufficient.

If you arrived here with a specific question, the spoke pages linked throughout this pillar will answer it in depth. If you want the full picture, read through the sections above and follow the threads that interest you. Bitcoin is complex, but every piece is knowable.

Back to bitcoin