Transactions are defined using a Forth-like scripting language.[3]:ch. 5 Transactions consist of one or more inputs and one or more outputs. When a user sends bitcoins, the user designates each address and the amount of bitcoin being sent to that address in an output. To prevent double spending, each input must refer to a previous unspent output in the blockchain.[67] The use of multiple inputs corresponds to the use of multiple coins in a cash transaction. Since transactions can have multiple outputs, users can send bitcoins to multiple recipients in one transaction. As in a cash transaction, the sum of inputs (coins used to pay) can exceed the intended sum of payments. In such a case, an additional output is used, returning the change back to the payer.[67] Any input satoshis not accounted for in the transaction outputs become the transaction fee.[67]

Bitcoins may not be ideal for money laundering, because all transactions are public.[50] Authorities, including the European Banking Authority[51] the FBI,[23] and the Financial Action Task Force of the G7[52] have expressed concerns that bitcoin may be used for money laundering. In early 2014, an operator of a U.S. bitcoin exchange, Charlie Shrem, was arrested for money laundering.[53] Subsequently, he was sentenced to two years in prison for "aiding and abetting an unlicensed money transmitting business".[43] Alexander Vinnik, an alleged owner of BTC-e was arrested in Greece July 25 of 2017 on $4 bln money laundering charges for flouting anti-money laundering (AML) laws of the US. A report by UK's Treasury and Home Office named "UK national risk assessment of money laundering and terrorist financing" (2015 October) found that, of the twelve methods examined in the report, bitcoin carries the lowest risk of being used for money laundering, with the most common money laundering method being the banks.[54]

The domain name "" was registered on 18 August 2008.[15] In November 2008, a link to a paper authored by Satoshi Nakamoto titled Bitcoin: A Peer-to-Peer Electronic Cash System[5] was posted to a cryptography mailing list. Nakamoto implemented the bitcoin software as open source code and released it in January 2009.[16][17][10] Nakamoto's identity remains unknown.[9]