Smart Contracts

DeFi, smart contracts, dApps, and DAOs — software replacing middlemen.

Updated Jun 22, 2026Reviewed by GaiaEx Academy Editorial

In this lesson

What a smart contract is
Why immutability matters

Key takeaways

1A smart contract is self-executing code on a blockchain
2It runs exactly as written when conditions are met
3Once deployed it's very hard to change — bugs are costly

Lesson summary

A smart contract is code that runs on a blockchain and follows predefined rules.

Mental model

Smart Contracts in plain terms

A smart contract is code that runs on a blockchain and follows predefined rules. It is powerful because users can verify and execute shared logic without trusting a private server.

Treat smart contracts as a tool for making a decision, not a term to memorise for its own sake.

What a smart contract is
Why immutability matters

Mechanics

How to reason about smart contracts

Contracts hold state, receive transactions, and update balances or permissions.

Once deployed, many contracts are hard to change unless an upgrade path exists.

Users interact by signing transactions from wallets or applications.

The reason these steps matter in practice is simple: a smart contract is self-executing code on a blockchain.

A smart contract is self-executing code on a blockchain
It runs exactly as written when conditions are met
Once deployed it's very hard to change — bugs are costly

Example

Smart Contracts, applied

An automated market maker contract can hold two tokens and quote swap prices from its reserves without a human market maker approving each trade.

If the example only works with these exact details, you have memorised a case rather than learned smart contracts.

Ask what you would need to see on screen or on chain to trust a smart contracts outcome before you act on it.

RememberDecision rule: Ask whether the contract is immutable, upgradeable, audited, and battle-tested before relying on it.

Common mistakes

What to unlearn about smart contracts

Readable code is not the same as safe code. A transparent bug is still a bug, and attackers can read it too.

Catch the smart contracts version early by asking which evidence would prove the claim, then actually looking for it.

Most costly smart contracts errors are not exotic; they are this ordinary shortcut repeated under time pressure.

Risk notes

Reading the risk in smart contracts

Reentrancy, bad access control, unsafe upgrades, and unlimited token approvals are common smart-contract failure modes.

Risk in smart contracts grows when markets move fast, liquidity thins, or an interface hides the warning that actually matters.

None of this means avoid smart contracts; it means using it with eyes open and a clear exit if you are wrong.

Explain what executes the rule.
Check whether upgrades are possible.
Review approvals before signing.

Practice

Turn smart contracts into a habit

Lock in Smart Contracts by applying it once — choose a real Decentralization example and walk it through the checks below.

Write your smart contracts answers as specific, testable sentences; if a sceptic could not challenge them with evidence, they are still too vague.

Explain what executes the rule.
Check whether upgrades are possible.
Review approvals before signing.

Review

Key terms

Blockchain: A shared, append-only ledger replicated across many computers, secured by cryptography and consensus.
DeFi: Decentralized Finance — permissionless, composable financial services built on smart contracts.
Smart Contract: Self-executing code on a blockchain that runs exactly as written when conditions are met.
Market Maker: A participant that continuously quotes buy and sell prices to provide liquidity.
Consensus Mechanism: The process by which a distributed network agrees on the valid state of the ledger (e.g. PoW, PoS).

Source notes