This book is a direct result of the NATO Advanced Study Institute held in Banyuls-sur-mer, France, June 1985. The Institute had the same title as this book. It was held at Laboratoire Arago. Eighty lecturers and students from almost all NATO countries attended. The purpose was to review the state of the art of physical oceanographic numerical modelling including the parameterization of physical processes. This book represents a cross-section of the lectures presented at the ASI. It covers elementary mathematical aspects through large scale practical aspects of ocean circulation calculations. It does not encompass every facet of the science of oceanographic modelling. We have, however, captured most of the essence of mesoscale and large-scale ocean modelling for blue water and shallow seas. There have been considerable advances in modelling coastal circulation which are not included. The methods section does not include important material on phase and group velocity errors, selection of grid structures, advanced methods to conservation in highly nonlinear systems, inverse methods and other important ideas for modern ocean modelling. Hopefully, this book will provide a foundation of knowledge to support the growth of this emergent field of science. The NATO Advanced Study Institute was supported by many organi- zations. The seed money, of course, was received from the NATO Science Commi ttee. Many national organizations provided travel money for partiCipants. In France, CNES, IFREMER, and CNRS provided funds to support the French participants. In the U. S.