Acts as a conduit allowing two processes to communicate Issues: Is communication unidirectional or bidirectional? In the case of two-way communication, is it half or full-duplex? Must there exist a relationship (i.e., parent-child) between the communicating processes? Can the pipes be used over a network? Ordinary pipes – cannot be accessed from outside the process that created it. Typically, a parent process creates a pipe and uses it to communicate with a child process that it created. Named pipes – can be accessed without a parent-child relationship.