Bitcoin is the first decentralised digital currency: a way to send value directly between people over the internet without a bank, payment processor, or government in the middle. It launched in 2009 as open-source software that anyone can run.

It runs on a public ledger called a blockchain, secured by proof-of-work mining and the SHA-256 hash function, which makes coins practically impossible to counterfeit or spend twice. Its supply is capped in code at 21 million, and new issuance is cut in half roughly every four years — a fixed, predictable scarcity that has earned Bitcoin the nickname “digital gold.”

Bitcoin was created by a person or group writing under the pseudonym Satoshi Nakamoto, whose real identity is still unknown. In October 2008 Nakamoto published the whitepaper, “Bitcoin: A Peer-to-Peer Electronic Cash System,” and the first block — the genesis block — was mined in early January 2009.

Nakamoto developed Bitcoin and corresponded with early contributors until around mid-2010, then handed off the project and withdrew from public view. The coins Nakamoto mined in the earliest days — estimated near 1.1 million BTC — have never moved.

The network is a peer-to-peer system in which thousands of computers (nodes) each keep an identical copy of the blockchain — a chronological record of every transaction. Transactions are bundled into blocks, and each block references a cryptographic hash of the one before it, forming a chain that cannot be altered without redoing all the work after it.

About every ten minutes, miners compete to solve a computational puzzle; the winner adds the next block and earns newly issued bitcoin plus transaction fees. No single party controls the system — changes require broad consensus among users, miners, and developers. Owners control their coins with private keys, and the smallest unit is the satoshi (0.00000001 BTC).

Bitcoin’s security rests on the SHA-256 cryptographic hash function — the same family of algorithm used across government and internet infrastructure. Miners must repeatedly run SHA-256 to find a valid hash for each new block, and the function underpins the digital signatures that prove ownership and authorise spending.

SHA-256 is collision- and preimage-resistant: it is computationally infeasible to reverse an output back to its input or to find two inputs with the same output. That property is what makes forging coins or rewriting history impractical.

Proof-of-work is energy-intensive by design — that expenditure is what secures the network. Critics point to electricity use comparable to a mid-sized country and the carbon footprint when that power comes from fossil fuels.

Supporters argue the cost is the price of a globally secure, decentralised monetary network, and that miners’ relentless hunt for the cheapest power pushes them toward stranded or surplus renewables and toward capturing otherwise-flared methane — sometimes helping balance grids and monetise wasted energy.

Securing Bitcoin means protecting your private keys. The maxim is “not your keys, not your coins”: whoever holds the keys controls the coins. Keys and seed phrases are safest kept offline, away from internet-connected devices.

Hardware wallets — physical devices that store keys offline and require manual confirmation — offer the strongest protection for long-term storage. Software wallets are convenient but demand strong passwords, two-factor authentication, and updates. Leaving coins on an exchange means trusting a third party with your keys; failures such as Mt. Gox (2014) and FTX (2022) wiped out customer funds. Loss is permanent: a large share of all bitcoin is believed lost forever to forgotten keys and discarded drives, which is why backups and estate planning matter.

Bitcoin’s price moves sharply — a feature of a young, global, 24/7 asset rather than a defect. The main drivers are:

• Fixed supply, shifting demand: supply cannot expand to meet demand, so sentiment swings hit price directly.
• An always-open speculative market: it reacts instantly to news, regulation, and sentiment with no closing bell.
• Liquidity: still smaller than gold or major indices, so large “whale” orders can move price more.
• Macro sensitivity: increasingly responsive to interest rates, inflation data, and geopolitics.

Bitcoin solved the double-spending problem without a trusted intermediary, creating the first genuinely scarce digital asset — a 21-million cap enforced by transparent, unchangeable code. Its decentralisation makes it censorship-resistant: no government or company can freeze accounts or block transactions, which is especially valuable under unstable currencies or authoritarian regimes.

The “digital gold” comparison reflects shared traits — scarce, durable, not controlled by any state — while improving on gold by being easily portable (sent worldwide in minutes), highly divisible (100 million satoshis per coin), and instantly verifiable on-chain. ETF approvals and corporate treasury adoption have reinforced this narrative.

The supply cap is absolute: only 21 million BTC will ever exist. Scarcity is enforced over time by the halving — roughly every four years (210,000 blocks) the block reward is cut in half, steadily slowing new issuance.

Rewards went 50 BTC (2009) → 25 (2012) → 12.5 (2016) → 6.25 (2020) → 3.125 (April 2024), with the next halving expected around 2028 (~1.5625 BTC) and the last coins mined near 2140, after which miners earn fees alone. Each halving has historically preceded a major bull cycle, though the 2024 event was the first to coincide with spot ETFs and heavy institutional participation.

Holdings are spread across individuals, exchanges, institutions, corporations, and governments. The largest single holder is believed to be Satoshi Nakamoto (~1.1 million BTC), untouched since 2010 and effectively out of circulation.

Publicly traded companies hold BTC as a treasury reserve, spot-ETF issuers custody large amounts on behalf of investors, and several governments have become significant holders — mostly through criminal seizures, with some now weighing strategic reserves.

Bitcoin upgrades conservatively, favouring security and backward compatibility via soft forks.

• SegWit (2017) fixed transaction malleability, raised effective block capacity, and made reliable second layers possible.
• Taproot (2021) added Schnorr signatures, improving privacy and enabling more efficient, sophisticated scripts.
• Lightning Network is a second layer for instant, low-fee payments: funds are locked in channels, transacted off-chain, and settled on-chain only at the end — enabling micropayments in seconds.

Newer projects build on Bitcoin’s security and network effects without changing core rules. Ordinals (2023) inscribe data onto individual satoshis for NFT-like assets; the experimental BRC-20 standard uses inscriptions to issue fungible tokens; and BTCFi describes emerging efforts to use Bitcoin in decentralised-finance-style applications — yield, collateral, and Bitcoin-backed assets.

Spot Bitcoin ETFs let investors gain exposure through ordinary brokerage and retirement accounts without managing wallets or keys; their approval in the US and other markets was a milestone in regulatory acceptance. The trade-off versus direct ownership is custody: an ETF holds the BTC for you, whereas holding your own keys gives full control and full responsibility.

Corporate treasuries — pioneered by Strategy in 2020 — convert cash into BTC as a hedge against currency debasement, accepting balance-sheet volatility in return. Governments have moved from hostility toward regulation and, in places, strategic interest: El Salvador adopted BTC as legal tender, the EU’s MiCA framework formalised oversight, and several jurisdictions are debating reserves.