Publisher Summary This chapter reviews the concept of traffic engineering (TE) as applied to IP traffic in the Internet. TE is all about discovering the other paths and links that are available in the network, whether the current traffic usage is within the network, and directing traffic to routes other than the shortest one so that optimal use is made of the resource in the network. This is achieved by a combination of extensions to the existing Interior Gateway Protocol (IGP) routing protocols, traffic monitoring tools, and traffic routing techniques, respectively. Traffic engineering is a familiar concept to town planners and road safety engineers—they are concerned with the ways to get the best flows of vehicles through congested streets with the minimum number of accidents. The significant traffic management can be usefully performed within the core of the network where the traffic volumes are greater. Here, individual flows from host to host can be bundled together and treated in the same way for forwarding down routes that are not necessarily the shortest. The easiest way to handle this is through a process known as tunneling.