Blockchain is a constantly updated list of transactions which resides across multiple computer devices, generally spread across locations or regions. With blockchain, many people can write entries into a record of information, and a community of users can control how this record of information is amended and updated. Like Wikipedia entries, no one person controls the information. This also eliminates the need for a central trust authority such as a bank. Thus, blockchain, in effect, acts as a secure, public ledger system removing the need for an intermediary. Blockchain is the underlying technology behind Bitcoin, Ethereum and other cryptocurrencies.