Bitcoin is the first decentralized crypto coin ever built on a block chain. It was created as an open source project by an anonymous person or group of people with the nickname Satoshi Nakamoto in 2009. To understand the Bitcoin block chain, we can imagine a book in which each page number contains a signature that can validate the contents of this and the previous page. This signature is calculated by an algorithm known as SHA-256 and cannot be reversed. In other words, we can compute the A-256 signature from a content, but we cannot obtain content if we know its SHA-256 signature. Back to the book, for example: If we tear out a page from the book, we can easily understand that a page is missing. The same applies to adding a page that does not exist. All pages are copied between the members of the chain, and for this reason the Bitcoin block chain is considered a distributed network. Bitcoin is an open source project maintained by a development team of over 580 active contributors. The code of the chain is available on Github. The main purpose of Bitcoin was to provide decentralized, but trusted, low-cost financial transactions between people and businesses around the world. Today, over 100,000 providers accept Bitcoin for payments. And there are between 2.9 and 5.8 million individual users who actively use Bitcoin crypto wallets. The price of Bitcoin can be very volatile due to speculation and has changed by more than +/- 20% during a single transaction in the past.