Blockchain is a foundational technology for the cryptocurrency ecosystem, serving as the engine behind Bitcoin and the reason Ethereum smart contracts hold value by offering a decentralized and trustworthy network for recording data and transactions. Unlike traditional ledgers managed by central authorities like banks, blockchain is a distributed digital ledger maintained by a global network of computers (nodes), each running the same software to store, manage, and verify a copy of the ledger. Transactions are added by users through accounts identified by public keys, with private keys serving as digital signatures. Pending transactions are grouped into blocks and verified by each node, ensuring changes are redundantly checked before being added to the chain. There are various ways to design blockchains, each with its own trade-offs in terms of openness, consensus mechanisms, and features like security and scalability. Blockchain offers numerous benefits, including security, immutability, reliability, and peer-to-peer transactions without intermediaries, making it a highly secure infrastructure for economic exchanges. It creates value by enabling independent financial ecosystems, processing smart contracts, tokenizing assets, and serving as an immutable record for important data. Blockchain can also function as a middleware to facilitate secure data sharing between organizations without storing sensitive information on the blockchain itself.