What Is Bitcoin? A Plain-English Introduction

Bitcoin is a digital currency that runs without a central issuer. No government, central bank, or company creates it or controls the network. It was described in a short paper published in October 2008 under the pseudonym Satoshi Nakamoto, and the network started running in January 2009. Whatever you think of it as an investment, it is worth understanding what it is mechanically, because most of the arguments for and against it follow from those mechanics.

The problem Bitcoin set out to solve

Digital money normally depends on a trusted record-keeper. When you send ₹1,000 through a bank transfer or UPI, banks keep the ledger that says your balance went down and the recipient's went up. Without a trusted ledger, digital money has an obvious weakness: a digital file can be copied, so what stops someone from spending the same coin twice? The Bitcoin paper's central idea was a way to prevent this 'double spending' without a central record-keeper, by having many independent computers agree on a single shared history of transactions.

The ledger and the miners

Bitcoin's ledger is a blockchain: a chain of blocks, each containing a batch of transactions and a cryptographic fingerprint (a hash) of the block before it. Thousands of computers around the world, called nodes, keep copies of this chain and check that new transactions follow the rules — for example, that nobody spends coins they do not have.

New blocks are added by miners. To add a block, a miner must find a number that, combined with the block's contents, produces a hash meeting a difficulty target. The only way to find it is trial and error, which requires enormous amounts of computing power and electricity. This system is called proof of work. Because each block's hash depends on the previous block, rewriting an old transaction would mean redoing the work for that block and every block after it, faster than the rest of the network adds new ones — which becomes practically impossible as the network grows.

What happens when you send bitcoin

Suppose you send a small amount of bitcoin to a friend. Your wallet creates a message saying, in effect, 'move this amount from my address to theirs', and signs it with your private key. The signature proves the instruction came from whoever controls that address without revealing the key itself. The wallet broadcasts the signed transaction to the network, where nodes check that the signature is valid and that the coins have not already been spent. Valid transactions wait in a pool until a miner includes them in a block, usually prioritising those that pay higher fees. Once the transaction is in a block, and especially once several more blocks have been added on top of it, it is treated as settled.

Two practical consequences follow. Transaction fees are not fixed; they rise when many people want to transact at once. And confirmation is not instant in the way a card payment appears to be — a new block is added roughly every ten minutes on average, so settlement takes minutes rather than seconds.

Why there will only ever be 21 million bitcoin

Miners who add a valid block receive newly created bitcoin as a reward, plus fees paid by the transactions in that block. The software halves the block reward roughly every four years (every 210,000 blocks), an event known as 'the halving'. The most recent halving took place in April 2024. Because the reward keeps halving, the total supply approaches a hard limit of 21 million coins, with the last fractions expected to be created around the year 2140.

This fixed, predictable supply is the feature supporters most often emphasise, contrasting it with currencies whose supply central banks can expand. Critics point out that a fixed supply does not by itself create value, and that changing the rules would require agreement across the network — which is part of what makes the cap credible, but also what makes the system slow to change.

What gives bitcoin a price

A share represents a claim on a company's future profits, and a bond on its future interest payments. Bitcoin has no profits, interest, or cash flows. Its price is set entirely by what buyers will pay and sellers will accept, influenced by adoption, regulation, interest rates and liquidity conditions, investor sentiment, and the activities of large holders. Because there is no cash flow to anchor a valuation, estimates of what bitcoin is 'worth' vary enormously, and its price has historically been far more volatile than that of major stock indices, with several falls of more than half from previous peaks.

Keys, wallets, and custody

Owning bitcoin really means controlling a private key, a long secret number that authorises spending from a particular address. A wallet is software or hardware that stores keys and creates transactions. There are two broad ways to hold bitcoin.

• Self-custody: you hold your own keys, usually protected by a recovery phrase. Nobody can freeze your coins, but nobody can recover them either. If the phrase is lost or stolen, the coins are effectively gone.
• Custodial: a crypto exchange or platform holds the keys on your behalf, and you see a balance in your account. It is more convenient, but you depend on that platform's security, solvency, and honesty. Several large exchanges worldwide have collapsed or been hacked, and customers have lost funds.

Bitcoin transactions cannot be reversed once confirmed. There is no bank helpline that can claw back a payment sent to the wrong address or to a scammer. This makes bitcoin a frequent tool in frauds, including fake investment schemes promising guaranteed returns.

Bitcoin in India

The Reserve Bank of India has repeatedly cautioned users, holders, and traders of virtual currencies, including in December 2013 and December 2017, highlighting economic, financial, operational, legal, customer-protection, and security risks, and stating that it had not licensed any entity to deal in them. India also taxes income from transferring crypto assets under a separate regime for 'virtual digital assets', and crypto platforms have been brought under anti-money-laundering reporting rules. These rules have changed several times and may change again, so check the current position with the Income Tax Department and other official sources before acting on any older summary.

Bitcoin is also distinct from the digital rupee being developed by the RBI. A central bank digital currency is legal tender issued by the central bank; bitcoin is not issued or backed by anyone.

Questions worth asking before buying any crypto asset

• Could I tolerate this holding falling by more than half, possibly for years?
• Who holds the keys, and what happens if that platform fails?
• Am I being promised guaranteed or fixed returns? (A strong warning sign of fraud.)
• Do I understand the current tax and reporting rules that apply to me?
• Am I buying because I understand it, or because its price has just risen sharply?