The limiting influence of the environment on sonar has long been recognised as a major challenge to science and technology. As the area of interest shifts towards the littoral, environmental influences become dominant both in time and space. The manifold challenges encompass prediction, measurement, assessment, and adaptive responses to maximize the effectiveness of systems. Although MCM and ASW activities are dominated in different ways and scales by the environment, both warfare areas have had to consider the significantly changing requirements posed by operations in the littoral. The fundamental scientific issues involved in developing models relating acoustics to the environment are matched in difficulty by the need for data for their validation and eventual practical use for prediction. In many instances the need is for the longer term planning activities. This book and the enclosed CD-ROM are the proceedings of a conference organised by the SACLANT Undersea Research Centre, and held at the Villa Marigola, Lerici, Italy, on 16-20 September 2002. This volume contains a CD-ROM which in addition to an electronically searchable version of the proceedings, has full colour versions of figures which are printed in black and white in the book.