What Is a Blockchain? A Beginner's Guide

At a glance

• A blockchain is a shared record of transactions, held and updated by many computers at once, that no single party can quietly change.
• Transactions are grouped into “blocks,” each cryptographically linked to the one before, which makes the history extremely hard to alter.
• “Decentralised” means no single entity is in charge: no single point of failure, and no one who can unilaterally rewrite the record.
• The network agrees on new entries through consensus, replacing the need for a trusted middleman like a bank.
• Bitcoin was the first major use of a blockchain; Ethereum made the idea programmable, enabling applications and DeFi.
• A blockchain records ownership but doesn't hold your coins for you, and confirmed transactions generally can't be reversed.

A shared record

Start with the simplest version. A blockchain is a ledger, a record of transactions, but instead of being kept by one bank or company, identical copies are held and updated by many computers around the world at the same time.

Because everyone holds the same copy, there's no single master version that one party controls. If someone tried to alter their copy, it would no longer match everyone else's, and the network would reject it. That shared, agreed record is the heart of the idea, and the reason a blockchain doesn't need a central authority to be trusted.

Why it's called a “chain of blocks”

The name describes how the record is built. Transactions are grouped together into “blocks.” Each new block is then linked to the one before it using cryptography, forming a chain that runs all the way back to the very first block.

This linking is what makes the record so hard to tamper with. Because each block is tied to the previous one, changing an old transaction would break the chain from that point forward, and you'd have to redo every block after it, on most of the network's computers, faster than the rest of the network keeps adding new ones. In practice that's prohibitively difficult, which is what makes a blockchain's history effectively permanent.

How a transaction gets added

When a transaction happens, it's broadcast to the network. The computers maintaining the blockchain check that it's valid, that it follows the rules and that the sender is authorised, and then it's included in the next block.

The network has to agree before a block is added, through a process called consensus. This is the step that replaces the trusted middleman: instead of a bank confirming a transaction, the network collectively confirms it. Different blockchains use different consensus methods, but the principle is the same: agreement across many participants, rather than a decision by one authority.

What “decentralised” really means

“Decentralised” is the word you'll hear most about blockchains, and it has a specific meaning: no single entity is in charge. The record isn't stored in one place or controlled by one company, but distributed across many independent participants.

This matters for two reasons. There's no single point of failure, no one server that can be switched off to bring the system down, and no single party that can unilaterally rewrite the rules or the history. That's the structural feature behind crypto's core promise: a system you don't have to trust a central institution to operate, because its integrity comes from the network itself.

Blockchain and Bitcoin

The first and best-known blockchain is Bitcoin's. As we explain in how Bitcoin works, Bitcoin uses a blockchain to record every transaction and to release new coins through mining, secured by the consensus process described above.

It's worth keeping the two ideas distinct, though. Bitcoin is a cryptocurrency; blockchain is the underlying technology it runs on. Bitcoin was the first major application of a blockchain, but, as it turned out, far from the only one.

Beyond currency

Once you can keep a shared, tamper-resistant record without a central authority, you can do more than track a currency. Ethereum extended the idea by making its blockchain programmable, so it can run applications, not just record payments.

That opened the door to a wide ecosystem, including decentralised finance, where financial services run directly on a blockchain. The common thread across all of it is the same shared, decentralised record, the foundation that everything else in crypto is built on.

What a blockchain doesn't do

It's just as useful to know the limits. A blockchain records transactions and ownership, but it doesn't, by itself, hold your coins for you, your crypto wallet holds the keys that prove what's yours on the chain.

A blockchain also doesn't make transactions reversible or guarantee that what's recorded is wise. Once something is confirmed, it generally can't be undone, which is a strength for integrity, but means mistakes (like sending to the wrong address) usually can't be reversed. Understanding what the technology does and doesn't protect you from is part of using it sensibly.

What to remember

A blockchain is a shared, decentralised record of transactions, maintained by many computers and linked together so its history is extremely hard to alter. It replaces a trusted central authority with agreement across a network, and that single idea is what makes cryptocurrencies possible.

Bitcoin was the first use of it; Ethereum and decentralised finance are later ones. If you'd like to go from understanding the technology to using it on a supervised Swiss platform, how to buy Bitcoin in Switzerland walks through the steps, and our Registration page shows how Eti-Tech is set up and supervised.