Turing completeness, named after mathematician Alan Turing, refers to a system that can perform any computation that any other programmable computer can, given enough time and memory. In blockchain, it describes a platform's ability to execute arbitrary programs.
Turing Complete Blockchains
Ethereum was the first major Turing-complete blockchain. Its smart contract platform (EVM — Ethereum Virtual Machine) can execute any computable function, enabling complex DApps, DeFi protocols, and programmable financial instruments.
Bitcoin's Limitations
Bitcoin's scripting language is deliberately not Turing complete. It supports basic conditions (multi-signature, time locks) but cannot run loops or complex programs. This was a design choice for security — limiting the scripting language reduces the attack surface.
Why It Matters
Turing completeness is what enables the rich ecosystem of smart contracts, DeFi, NFTs, and DAOs. Without it, a blockchain can only handle simple transfers. However, greater programmability also introduces more potential for bugs and exploits.