Bidirectional transmission over optical fibre networks may yield a large cost reduction because of the reduction of the network infrastructure by a factor two and the potential cost reduction by an integrated transceiver design. It may also provide a cost-effective way to upgrade distribution networks by adding bidirectional channels. This book provides an overview of bidirectional transmission in optical networks. It handles: physical aspects - the behaviour of the fibre itself in bidirectional transmission; transmission aspects - the behaviour and design of bidirectional systems; and network aspects - the influence of bidirectional transmission on network design. Practical guidelines are also given for bidirectional system design. This book is aimed at designers, builders and operators of optical networks, such as the manufacturers of optical transmission systems, public-network operators, developers of local-area networks and cable-television operators. The intended level of readership is graduate level in physics or electrical engineering.