Blockchain technology is fundamental to the crypto space. It acts as the secure and transparent public ledger that underpins cryptocurrencies like Bitcoin. Here's how blockchain makes cryptocurrencies function:

Security: Transactions are encrypted and chronologically linked together in blocks, making them nearly impossible to tamper with. This creates a very secure system compared to traditional financial institutions.
Decentralization: Blockchain eliminates the need for a central authority to verify transactions. Instead, a network of computers maintains the ledger, removing a single point of failure and reducing the risk of fraud.
Transparency: All transactions are publicly viewable on the blockchain, fostering trust and immutability. Anyone can verify the history of a coin and see exactly where it's been.
Faster Settlements: Compared to traditional systems, blockchain can significantly speed up transaction settlements, especially for international transfers.

In short, blockchain provides the critical infrastructure for cryptocurrencies to function as a secure, decentralized, and transparent form of digital money.