Blockchain is a distributed ledger technology that allows for real-time, transparent transactions between counterparties without intermediaries. It replaces traditional clearinghouse and reconciliation models by giving all counterparties a shared real-time ledger where transactions are applied simultaneously. This reduces costs and risks compared to current systems. Blockchain ledgers are robust due to cryptography and distribute networks, and make tampering difficult. A variety of public and private blockchain applications are emerging for areas like finance, legal contracts, trade, and digital assets. However, challenges remain around system risks, regulation, and realizing cost savings.