This chapter presents a comprehensive survey on various works done in the field of wavelength division multiplexing based optical networks. We start with a brief introduction of lightpath establishment in optical networks, and then move to different routing algorithms that are used for finding a end-to-end route between a source-destination pair. Thereafter, this chapter presents different wavelength assignment policies for lightpath establishment and compares them. Furthermore, the traffic grooming mechanisms are presented for better utilization of network resources. Finally, this chapter explores the fault management techniques that are used for recovery purpose.