This chapter continues the survey of telecom and networking technologies that are applicable to enterprise environments, by focusing on metropolitan area networks (MANs) and briefly on wide area networks (WANs). We briefly discussed MANs in the previous chapter, but did so from a metro Ethernet perspective; the discussion here is more general. Networking is part of the technology architecture that defines the infrastructure resources of an enterprise. Some of the technologies described here are applicable to service providers. However, savvy enterprise architects can also put these networking technologies to work for them-understanding what services are being deployed by carriers will enable enterprise planners to select new state-of-the-art capabilities that benefit the organization’s target vision. We focus here more on connectivity-level technologies or physical layer services rather than higher-layer logical services, e.g., IPv4 and IPv6, because the actual corporate communication disbursements depend almost directly on the type of physical layer services selected rather than on the upper-layer capabilities selected (e.g., Enhanced Interior Gateway Routing Protocol versus Open Shortest Path First.) We start out with a bottom-line section where readers interested in general trends for technology architecture planning for enterprise networks, specifically for MANs and WANs, can find some quick pointers. Then we proceed with an assessment of relevant technologies.