Smart contracts are self-executing programs stored on a blockchain that automatically enforce and execute the terms of an agreement when predefined conditions are met — without requiring any intermediary (bank, lawyer, escrow agent). Once deployed on the blockchain, a smart contract’s code is immutable and runs exactly as programmed, with outcomes that are transparent, verifiable, and irreversible.
Ethereum’s Vitalik Buterin popularised smart contracts as Ethereum’s core innovation. Solidity is the primary programming language for Ethereum smart contracts. They power virtually all DeFi protocols, NFT collections, DAOs (Decentralised Autonomous Organisations), token launches, and decentralised exchanges. A single complex DeFi protocol may consist of dozens of interlinked smart contracts handling billions of dollars.
Smart contracts eliminate: counterparty risk (no one can refuse to pay if conditions are met); intermediary fees; geographic restrictions; and settlement delays. However, they introduce smart contract risk — bugs in code are permanent and exploitable. High-profile hacks include the DAO hack (2016, $60M), the Ronin Bridge hack (2022, $625M), and dozens of smaller DeFi exploits. Professional security audits are essential before deploying or using any smart contract protocol.
Example: A smart contract on Uniswap automatically swaps your ETH for USDC at the best available price, sends you the USDC, and sends the ETH to the liquidity pool — all in one atomic transaction with no human involvement, completing in under 15 seconds.
Learn more: Ethereum.org — Introduction to Smart Contracts
