This article discusses the routing and wavelength assignment (RWA) problem in optical networks employing wavelenength division multiplexing (WDM) technology. Two variants of the problem are studied: static RWA, whereby the trac requirements are known in advance, and dynamic RWA in which connection requests arrive in some random fashion. Both point-to- point and multicast trac demands are considered. Keywords: Wavelength division multiplexing (WDM), Optical networks, Routing and wavelength assignment (RWA), Virtual topology design, Optical multicast