A major telecommunication vendor came up with the challenge of optimising network design and equipment selection in order to minimise overall network cost while performing quick network designs for commercial projects. From this challenge, this research project was open and, almost a year after, very interesting results were obtained which led to this thesis. Several perspectives and optimisation strategies were studied and this book describes a collection of the most interesting results regarding optimisation of regenerator placement and wavelength assignment in DWDM optical networks.