The static and semi-dynamic routing problems in the Wavelength Division Multiplexing (WDM) networks are generally very complicated. Finding the exact optima for most of these optimization problems is usually impossible with today's computation facility even for the medium size networks. Therefore, finding a sub-optimal solution within a reasonable computation time is the only choice, while knowing the proximity of the sub-optimal solution to the exact-optimum would be an additional advantage. Different from most of the existing heuristic approaches, this book provides strict formulations and mathematical solutions with polynomial complexities for various optimization problems, including Min-Cost Problem, Max-RWA Problem, Traffic Grooming Routing Problem, and Semi-Dynamic Optimization Problem. The results are compared with other state-of-the-art solutions, such as LP-relaxation and branch-and-bound methods. The solution framework provided in this book has been proven to be very computationally efficient, while generating results with good optimality, at the same time providing tight theoretical bounds. The computation time can be further reduced by reusing the optimized results.