The queueing systems considered in the preceding chapters had customers demanding service from a single facility. But there are many real-world systems in which customers get served in more than one station arranged in a network structure, which is a collection of nodes connected by a set of paths. In a queueing network, a group of servers operating from the same facility are identified as a node.As described in Chapter 1, under the historical perspective, a large portion of the advances occurring in queueing theory after the 1960s is connected to networks of queues one way or the other. Computer, communication, and manufacturing systems where queueing theory has found major application areas abound with such networks. This chapter provides an introduction to some simple queueing networks and their analysis.