Unix to Unix Copy Protocol ( UUCP ) is a protocol for transferring files between different computers, especially those with the Unix operating system. There are also doing the Unix shell command uucp = Unix to Unix Copy.

The connection between the computers is thereby built up only on demand or at regular intervals is called polling. Originally mainly ordinary telephone lines via modem or acoustic coupler were used. However UUCP supports virtually any type of transport medium, such as serial lines, X.25 or TCP / IP ( UUCP -over- IP). By UUCP node to forward files to other UUCP node, can also - similar to a mailbox network - computers can be achieved, for which no direct connection is established. About UUCP also e- mail can be transmitted. In addition, the Usenet was initially based on UUCP.

With the increasing popularity of the Internet in the late 1990s UUCP lost more and more important, it was mostly replaced by the POP and SMTP protocols. Today, it is still occasionally used to connect computers that have no direct connection to the Internet. The format of e- mails being sent over UUCP is described in RFC 976. The protocol itself is not the subject of an RFC.

Indicative of UUCP was the relative addressing of computers that resembled common in the Internet today purely visual, but had to be specified in the rule as a path towards the target computer, so including all intermediate nodes. These were compensated by exclamation mark ( bang slang ) separated from each other, which is why it was also called Bang Bang Path or addressing. Example: first, second knot knot knot third user! . This form of addressing was error-prone and cumbersome. It was therefore rapidly displaced by the availability of UUCP over TCP / IP by DNS-based addressing.