In this chapter, we explored several problems that are commonly modeled as networks, with nodes and arcs representing a variety of situations. These problems were the transportation, assignment, transshipment, maximal-flow, shortest-route, and minimal-spanning tree problems. Linear programming models were developed for all but the minimal-spanning tree, highlighting the fact that linear programming can be beneficial in many different areas. Computer software that takes advantage of the special structure of these problems can help solve large network problems very efficiently.