The papers at the General Symposia of the Joint Oceanographic Assembly were presented by authors who had been invited to deal with topics of broad interdisciplinary interest. Together they gave a valuable account of the present state of marine research, its proQlems and potential. There seems merit in publishing them in one volume and we are grateful to the authors who kindly agreed to prepare their papers for publication. This has taken some time (and not all authors found it possible) but we hope the resulting volume is still indicative of trends in modern oceanography. Particularly noticeable is the way in which the applied aspects are beginning to play a more important part in spite of worries about the effects of the Law of the Sea on our freedom to make observations. We are especially grateful to the four authors who agreed to give lectures summarising the work in their own field which was reported at the Assembly. We also wish to thank the other authors, as well as all concerned with the Assembly and with the production of this volume.