The technology that underpins the functionality of cryptocurrencies is blockchain technology. Blockchain is a decentralized and distributed ledger that records all transactions across a network of computers, ensuring transparency and security. Each block in the chain contains a list of transactions and is linked to the previous block, creating an unchangeable record. This structure prevents fraud and double-spending, making cryptocurrencies like Bitcoin and Ethereum secure alternatives to traditional currencies. Additionally, blockchain technology enables the development of smart contracts and decentralized applications, which broaden its applicability beyond just digital currencies.