Blockchain: A Beginner’s Guide

Blockchain is the technology behind Bitcoin, Ethereum and thousands of other crypto projects. But what exactly is a blockchain, and why is it useful?

At its core, a blockchain is a shared digital record of transactions or other data maintained across a network of computers. Instead of relying on one central organization to maintain the database, blockchain networks can allow many independent participants to verify and maintain a common record.

In this guide, you’ll learn how blockchains work, why they can be difficult to alter, how networks reach agreement, and why different blockchains use different approaches.

What Is a Blockchain?

A blockchain is a type of distributed database or ledger that records information in a sequence of blocks.

Each block contains data and is cryptographically connected to the block before it. Together, these blocks form a chronological chain—hence the name blockchain.

On a cryptocurrency network, that data typically includes transactions. When someone sends cryptocurrency, the transaction can be broadcast to the network, verified according to the network’s rules and eventually included in a block.

Copies of the blockchain are maintained by computers participating in the network, commonly called nodes.

Because multiple participants maintain and verify the ledger, a public blockchain does not have to depend on a single company or database administrator to maintain its transaction history.

Ethereum, for example, describes its blockchain as a public database shared and updated across many computers, with blocks cryptographically referencing their predecessors.

How Does Blockchain Work?

The exact process differs between networks, but a simplified cryptocurrency transaction usually looks like this:

1. A transaction is created

A user requests a transaction, such as sending cryptocurrency from one address to another.

2. The transaction is broadcast

The transaction is sent to the blockchain network.

3. The transaction is verified

Network participants check whether the transaction follows the protocol’s rules. For example, the network must prevent someone from spending cryptocurrency they don’t control.

4. Transactions are included in a block

Valid transactions can be grouped into a new block.

5. The network reaches agreement

The blockchain’s consensus mechanism determines how participants agree on valid blocks and the current state of the network.

6. The blockchain is updated

Once accepted according to the network’s rules, the new block becomes part of the blockchain’s history.

The details vary considerably. Bitcoin uses proof of work and mining, while Ethereum currently uses proof of stake and validators.

Why Are Blocks Connected?

The connection between blocks is one of blockchain’s most important characteristics.

Each block contains information that cryptographically references the previous block. Changing historical information can therefore affect the cryptographic relationship between that block and the blocks that follow it.

That doesn’t mean every blockchain is literally “impossible to change.” That’s an oversimplification you’ll often encounter in crypto.

The practical difficulty of altering blockchain history depends on the network’s consensus mechanism, security, decentralization and other factors.

On Bitcoin, for example, proof of work builds upon previous blocks. Rewriting older transactions would require recreating the required work for subsequent blocks while competing with the rest of the network.

A better way to think about it is:
Blockchains are designed to make accepted transaction history difficult to alter without the network detecting or rejecting the change.

What Is Blockchain Consensus?

If thousands of independent computers maintain copies of the same ledger, they need a way to agree on which version is valid.

That’s the job of a consensus mechanism.

Consensus mechanisms establish rules that allow network participants to agree on valid transactions, blocks and the state of the blockchain.

Two of the best-known approaches are:

Proof of Work

Proof of Work (PoW) uses computational work to secure the network and produce valid blocks.

Bitcoin is the best-known example.

Miners compete to find valid blocks using specialized computing equipment. Successful miners can receive newly issued bitcoin and transaction fees as rewards.

Proof of Stake

Proof of Stake (PoS) uses cryptocurrency committed—or staked—by validators as part of the mechanism for securing the network.

Ethereum uses proof of stake. Validators participate in proposing and verifying blocks, while protocol rules can penalize certain dishonest behavior.

Neither mechanism should simply be described as universally “better.” They make different design and security trade-offs.

Public vs Private Blockchains

Not every blockchain works like Bitcoin.

Public Blockchains

Public blockchains generally allow anyone to view the ledger and interact with the network according to its protocol rules.

Examples include Bitcoin and Ethereum.

Their goal is typically to operate without requiring one central organization to control the ledger.

Private Blockchains

Private blockchains restrict participation or access.

A company or group of organizations may determine who can interact with the network, validate transactions or access certain information.

This sacrifices some of the openness associated with public blockchains but can make sense for particular business or institutional applications.

Permissioned Blockchains

A permissioned blockchain restricts certain network activities to approved participants.

The distinction isn’t always simply public vs private. Blockchain designs can combine different levels of visibility, control and participation.

Why Is Blockchain Used in Crypto?

Before Bitcoin, digital money faced a fundamental challenge: how can participants agree on ownership and prevent the same digital value from being spent twice without relying on a central authority?

Bitcoin combined several existing technologies and economic incentives into a system where a distributed network could maintain a shared transaction history.

Blockchain provides cryptocurrencies with infrastructure for recording and verifying ownership transfers.

Different networks have since expanded the concept far beyond simple payments.

Ethereum, for example, supports programmable smart contracts, allowing developers to build decentralized applications and financial protocols on top of the network.

That has led to areas such as:

• Decentralized finance (DeFi)
• Stablecoins
• NFTs
• Blockchain gaming
• Tokenization
• Decentralized applications
• Digital identity systems

Blockchain therefore isn’t a cryptocurrency itself. It is underlying infrastructure that cryptocurrencies and blockchain applications can use.

Are All Blockchains Decentralized?

No.

Blockchain and decentralization are related concepts, but they are not the same thing.

A network can technically use blockchain technology while still having significant control concentrated among a relatively small number of organizations or participants.

Decentralization can involve several dimensions, including:

• Who validates transactions
• Who operates nodes
• How concentrated ownership is
• Who controls software development
• How governance decisions are made
• Whether users need permission to participate

This is why simply describing a project as “blockchain-based” doesn’t tell you how decentralized it actually is.

What Are the Advantages of Blockchain?

Depending on its design and use case, blockchain technology can offer several useful characteristics:

• Transparency: Public blockchains can allow anyone to inspect transaction history.
• Verifiability: Participants can independently verify information recorded by the network.
• Reduced dependence on intermediaries: Some blockchain applications allow users to transact without relying on a traditional central intermediary.
• Programmability: Smart-contract networks can automatically execute predefined rules.
• Global accessibility: Public blockchain networks can generally be accessed from anywhere with an internet connection and appropriate software.

However, these benefits come with trade-offs.

What Are the Limitations of Blockchain?

Blockchain isn’t automatically the best solution for every problem.

Common limitations can include:

• Scalability: Some networks can process far fewer transactions than centralized payment infrastructure.
• Transaction costs: Network fees can become expensive during periods of heavy demand.
• Complexity: Wallets, private keys, network fees and blockchain transactions can be confusing for beginners.
• Irreversible mistakes: Depending on the network and situation, sending assets to the wrong address may be extremely difficult or impossible to reverse.
• Security risks: A blockchain protocol can be secure while applications, bridges, wallets or smart contracts built around it contain vulnerabilities.
• Decentralization trade-offs: Increasing speed or convenience can sometimes involve greater centralization.

Understanding these trade-offs is much more useful than treating blockchain as either a solution to everything or a technology with no value.

Explore Our Blockchain Guides

Understand blockchain technology from the ground up, including blocks, transactions, nodes and consensus.

Compare two major blockchain consensus mechanisms and understand how they secure crypto networks.

Learn how public, private and permissioned blockchains differ and where each model is used.

Discover what nodes do, why blockchain networks need them and how they help verify network data.

Understand how decentralized networks agree on transactions without relying on one central authority.

Learn when a blockchain transaction can be considered settled and why finality differs between networks.

Compare how blockchains and centralized databases store, verify and control information.

Continue Learning

Crypto Mining

Learn how proof-of-work networks such as Bitcoin use miners to process transactions and secure the blockchain.

Crypto Staking

Understand how proof-of-stake networks use validators and staked assets to help secure their blockchains.

Smart Contracts

Learn how programmable blockchain applications can execute rules and transactions automatically.

Blockchain FAQ

Is blockchain the same as Bitcoin?

No. Bitcoin is a cryptocurrency and network that uses blockchain technology. Blockchain is the underlying method used to maintain Bitcoin’s transaction ledger. Many other networks also use blockchain technology.

Can blockchain be hacked?

There isn’t one universal answer. Security depends on the specific blockchain and what part of the ecosystem you’re talking about. Attacking a major blockchain’s consensus mechanism is very different from exploiting a vulnerable smart contract, stealing a private key or compromising an exchange account.

Can blockchain transactions be reversed?

Usually, there is no traditional chargeback mechanism once a cryptocurrency transaction has been finalized on a public blockchain. The exact meaning and timing of finality varies by network.

Who controls a blockchain?

It depends on the blockchain. Public networks may distribute responsibilities among developers, node operators, miners or validators, token holders and users. Private blockchains can have much more centralized control.

Do all cryptocurrencies use a blockchain?

Not necessarily. Blockchain is the dominant architecture behind cryptocurrencies, but distributed-ledger systems can use other structures.

Why does blockchain need cryptocurrency?

Not every blockchain necessarily needs a publicly traded cryptocurrency. On many public networks, however, the native asset plays an important economic role—for example, paying transaction fees, rewarding miners or participating in staking.

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