This article provides insight into how Blockchains work. A block chain or Blockchain is a distributed database that maintains a continuously growing list of data records that are hardened against tampering and revision, even by operators of the data store's nodes. One can view a Blockchain as a public ledger of all transactions that have ever been executed. It is constantly growing as completed blocks are added to previous blocks forming a chain. Importantly, blocks are added to the Blockchain in a linear, chronological order. Each miner gets a copy of the Blockchain when joining the Bitcoin network. The Blockchain they receive has complete and accurate information about the addresses and their balances right from the genesis block to the most recently completed block. (c) 2016 Wiley Periodicals, Inc.