The technology of combining a number of optical wavelengths and then transmitting the same through a single fibre is called wavelength division multiplexing (WDM). Conceptually, the technology is similar to that of frequency division multiplexing (FDM) used in analogue transmission. Dense wavelength division multiplexing (DWDM) is anew born multiplexing technology in the fibre optic transmission, bringing about a revolution in the bit rate carrying capacity over a single fibre. The emergent of DWDM system is one of the important phenomena in development of optic fibre transmission. This article gives introduction of DWDM technology. The demand of bandwidth is increasing day by day, especially for data traffic. Service providers are required to provide the bandwidth dynamically and in shortest possible time. This can only be done by DWDM. In future advanced DWDM components will be available. Thus, it will be possible to manage the optical signal dynamically, which will allow more flexibility to the service providers.