This book arises from a NATO-sponsored Advanced Study Institute on 'The Role of Air-Sea Exchange in Geochemical Cycling' held at Bombann@§. near Bordeaux, France. from 16 to 27 September 1985. The chapters of the book are the written versions of the lectures given at the Institute. The aim of the book is to give a comprehensive up-to-date coverage of the subject. presented in a teaching mode. The chapters contain much recent research material and attempt to give the reader an understanding of how the role of air-sea exchange in geochemical cycling can be quantitatively assessed. In the last decade, major advances in the fields of marine and atmospheric chemistry have underlined the role of physical, chemical and biological processes at and near the air-sea interface in a number of geochemical cycles (C. S, N, metals etc ... ). Further, there is strong concern over the anthropogenic perturbation of these cycles on both regional and global scales. The first part of the book (Chapters 1 to 8) provides a review of topics fundamental to such studies. These topics include concepts in geochemical modelling, assessment of atmospheric transport from sources to the oceans. description of mixing and transport processes within the ocean for both dissolved and particulate materials, quantification of air-sea fluxes for both gases and particles, photochemical transformations in the atmospheric and oceanic boundary layers.