A blockchain is a ledger of transactions shared across many computers, where data is grouped into blocks chained together through cryptography, which makes any later modification extremely difficult. No central authority keeps the ledger: the network participants validate additions.
Validation relies on a consensus mechanism. Proof of work (Bitcoin) requires solving energy-intensive computations; proof of stake (Ethereum since 2022) relies on participants who lock up tokens as collateral.
The first use case is Bitcoin, launched in 2009. Ethereum added smart contracts, programs executed on the blockchain, which enabled DeFi, NFTs and DAOs. There are also private blockchains, between identified partners, for traceability or interbank exchanges. The main challenges remain cost, speed (hence "layer 2" solutions) and regulation.
Why it matters when hiring
The blockchain talent pool is small and very international. Distinguish the smart contract developer (Solidity, Rust, contract security), the protocol engineer (cryptography, distributed systems) and the application developer who integrates a wallet. In an interview, a good signal is knowledge of classic smart contract vulnerabilities and audits. The trap: a profile who has mostly followed crypto news without having deployed code.