This chapter examines the basic technologies for optical networks. It discusses their applications in the networks. The fact that next generation communication networks face some challenging problems should be kept in mind. Such problems include: support of integrated service, real-time traffic support, and ability to handle exciting new applications such as desktop videoconferencing, interactive TV, supercomputer interconnection, and telemedicine. It also includes growth flexibility and fault tolerance and very high bandwidth requirements at low cost. The chapter first introduces such optical networks, which include fiber channel and fiber distributed data interface (FDDI) used as local area network (LAN), and synchronous optical network (SONET) deployed as a wide area network (WAN). In addition, it discusses other emerging technologies relating to optical networking, such as optical Gigabit Ethernet, dynamic synchronous transfer mode (DTM), and multiprotocol label switching (MPLS). The chapter also discusses fiber channel, a network technology for linking servers to storage systems that move data more efficiently than existing network pipes.