Blockchain

What Is a Blockchain?

A blockchain is a distributed, immutable digital ledger that records transactions across a decentralized network of computers. Each block contains a batch of verified transactions that are cryptographically linked to the previous block, forming a continuous and tamper-resistant chain. This structure ensures that once data is recorded, it cannot be altered without the consensus of the network, making blockchains one of the most secure and transparent data systems ever created.

The concept was first implemented in 2009 with the launch of Bitcoin, but blockchain technology has since expanded far beyond digital currency. Today, blockchains power lending protocols, decentralized exchanges, supply chain systems, and a wide range of financial applications collectively known as decentralized finance.

How Blockchains Work

At a high level, a blockchain operates through a repeating cycle of transaction broadcasting, validation, and permanent recording.

When a user initiates a transaction — such as sending cryptocurrency or interacting with a smart contract — that transaction is broadcast to the network. Nodes (computers running the blockchain software) collect pending transactions into a candidate block. The block then goes through a consensus process to determine its validity.

Consensus Mechanisms

The consensus mechanism is the set of rules that determines how the network agrees on which transactions are valid and which node gets to add the next block. The two most common approaches are:

• Proof of Work (PoW): Miners compete to solve a computationally intensive puzzle. The first to find a valid solution proposes the block and earns a reward. Bitcoin uses this model, which prioritizes security and decentralization at the cost of energy consumption.
• Proof of Stake (PoS): Validators are selected to propose blocks based on the amount of cryptocurrency they have staked as collateral. Ethereum transitioned to this model in 2022, significantly reducing its energy footprint while maintaining security.

Once a block is validated and added to the chain, every node updates its copy of the ledger. Because no single entity controls the ledger, there is no central point of failure — and no need for a trusted intermediary.

Immutability and Transparency

Each block contains a cryptographic hash of the previous block, creating an unbroken chain of references stretching back to the very first block (called the genesis block). Altering any historical block would invalidate every subsequent hash, making tampering immediately detectable. This immutability is what gives blockchains their trustworthiness: participants can independently verify the entire history of transactions without relying on any authority.

Types of Blockchains

Not all blockchains are alike. They generally fall into several categories:

• Public blockchains like Bitcoin and Ethereum are open and permissionless — anyone can participate as a node, validator, or user.
• Private blockchains restrict participation to approved entities, often used by enterprises for internal processes.
• Layer 2 networks are secondary chains or rollups built on top of a Layer 1 blockchain to improve speed and reduce transaction costs while inheriting the security of the base layer.

The choice of blockchain matters for DeFi users. Different networks offer varying tradeoffs in transaction speed, gas fees, security guarantees, and the ecosystem of protocols available.

Why Blockchains Matter for DeFi and Lending

Blockchains provide the trust and transparency layer that makes decentralized lending possible. When a borrower deposits collateral into a lending protocol, the blockchain records that deposit in a way that anyone can verify. Interest accrual, liquidation triggers, and loan repayments all execute on-chain through smart contracts, removing the need for banks or intermediaries.

This transparency also enables composability — different protocols can read each other's on-chain data and build on top of one another, creating the interconnected financial ecosystem sometimes called "money legos." A single blockchain transaction can involve borrowing from one protocol, swapping on a decentralized exchange, and depositing into a yield strategy, all in one atomic operation.

The Multi-Chain Landscape

The blockchain ecosystem has evolved from a single-chain world into a multi-chain environment. Ethereum remains the largest DeFi hub, but networks like Arbitrum, Optimism, Base, Polygon, and BSC host billions in lending activity. Cross-chain bridges allow assets and data to move between these networks, though they introduce their own security considerations.

For borrowers and lenders, this multi-chain reality means more options — and more complexity. Rates, liquidity, and protocol availability vary across chains, making it important to compare opportunities across the ecosystem.