**What technology underpins the concept of cryptocurrencies?**
The concept of cryptocurrencies is underpinned by blockchain technology. A blockchain is a decentralized, distributed ledger that records all transactions across a network of computers. Each block in the chain contains a list of transactions and is chronologically linked to previous blocks, ensuring data integrity and security. This technology enables trustless exchanges between parties, as transactions are verified and recorded through cryptographic hashes rather than relying on a centralized authority. Consequently, blockchain facilitates the operation of various cryptocurrencies, like Bitcoin and Ethereum.