What Is a Smart Contract? Self-Executing Code Explained

Defining Smart Contracts

A smart contract is a software program stored and executed directly on a blockchain. Nick Szabo originally coined the phrase in the 1990s, comparing a smart contract to a traditional digital vending machine:

"You insert coins, make a selection, and the machine automatically dispenses the item. There is no store clerk or escrow agent required; the mechanics of the machine enforce the agreement."

How They Execute on Chain

Smart contracts are typically authored in high-level languages like Solidity or Vyper, then compiled into EVM bytecode. When deployed, the bytecode is permanently assigned a cryptographic address on the blockchain.

// Simple Educational Escrow Interface
contract SimpleEscrow {
    address public arbiter;
    address public beneficiary;
    
    function release() public {
        require(msg.sender == arbiter, "Only arbiter can release");
        payable(beneficiary).transfer(address(this).balance);
    }
}

Core Benefits of Smart Contracts

• Autonomy: Execution does not rely on third-party legal enforcement or brokers.
• Determinism: Given the same input and state, the contract produces the identical output on every node on Earth.
• Composability: Contracts can interact with other contracts like building blocks (often termed "money legos").