Smart Contracts
What smart contracts are, how they work, writing in Solidity, the importance of audits, and how self-executing code powers DeFi, NFTs, and DAOs.
What Is a Smart Contract?
A smart contract is a program stored on a blockchain that automatically executes when specific conditions are met. Think of it like a vending machine: you insert money (input), the machine verifies the amount (condition), and dispenses your item (execution) — all without a human operator. Smart contracts work the same way but for financial agreements, token swaps, NFT mints, voting systems, and much more.
Once deployed to a blockchain, a smart contract's code is public and immutable — anyone can read it, and nobody (not even the creator) can change it. This transparency and predictability are what make smart contracts trustworthy. Instead of trusting a company to honor an agreement, you trust code that executes exactly as written.
What Can Smart Contracts Do?
- Automatically swap one token for another on a DEX when you click "Swap"
- Issue a loan when collateral is deposited, and liquidate it if the collateral value drops too low
- Mint a new NFT and record its ownership on-chain
- Distribute governance votes based on token holdings
- Release payment from escrow when both parties confirm delivery
Where Do Smart Contracts Run?
Smart contracts run on blockchains that support them — most importantly Ethereum, but also Solana, Avalanche, Polygon, Arbitrum, Base, and many others. Bitcoin's scripting language is intentionally limited, which is why most smart contract development happens on Ethereum and its ecosystem.
Key Takeaways
- Smart contracts are self-executing programs stored on a blockchain
- They run automatically when conditions are met — no human intervention needed
- Their code is public and immutable, providing transparency and trust
- Smart contracts power DeFi, NFTs, DAOs, and almost everything in modern crypto
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