Bitcoin is a payment system invented by Satoshi Nakamoto. He published the invention in 2008 and released it as open-source software in 2009. The system is peer-to-peer; users can transact directly without any middleman. The system works without a central repository or single administrator, which has led the US Treasury to categorize it as a decentralized virtual currency. Bitcoin is often called the first crypto currency. Bitcoin is better described as the first decentralized digital currency. It is the largest of its kind in terms of total market value. Bitcoin is an instrument of alternative finance, which has emerged outside of the traditional financial system.