Part I. Introduction: 1. The evolution of the Joint Global Ocean Flux Study project J. J. McCarthy; Part II. Carbon Exchange Processes and Their Variability: 2. Marine primary production and the effects of wind E. Sakshaug, K. Tangen and D. Slagstad; 3. Net production, gross production and respiration: what are the interconnections and what controls them? P. J. le B. Williams; 4. The role of iron in plankton ecology and carbon dioxide transfer of the global oceans H. J. W. de Baar and P. W. Boyd; 5. The influence of iron on ocean biology and climate: insights from the IronEx studies in the equatorial Pacific P. S. Liss and S. M. Turner; 6. Testing importance of iron and grazing in maintenance of the high nitrate condition in the equatorial Pacific Ocean, a physical-biological model study F. Chai, S. T. Lindley, J. T. Toggweiler and R. T. Barber; 7. Continental margin carbon fluxes K.-K. Liu, K. Iseki and S.-Y. Chao; 8. Sediment trap sampling in surface waters: issues and recommendations W. D. Gardner; Part III. Regional-Scale Analysis and Integration: 9. Mixed-layer dynamics and primary production in the Arabian Sea S. Sathyendraneth and T. Platt; 10. Plankton ecology and biogeography in the Southern Ocean: a review of the Southern Ocean JGOFS U. Bathmann, J. Priddle, P. Tregeur, M. Lucas, J. Hall and J. Parslow; 11. Process studies in eutrophic, mesotrophic and oligotrophic oceanic regimes within the tropical northeast Atlantic A. Morel; 12. The North Atlantic carbon cycle: new perspectives from JGOFS and WOCE S. C. Doney, D. W. R. Wallace and H. W. Ducklow; 13. Temporal studies of biogeochemical dynamics in oligotrophic oceans A. F. Michaels, D. M. Karl and A. H. Knap; Part IV. Global-Scale Analysis and Integration: 14. Advances in ecosystem modelling within JGOFS M. J. R. Fasham and G. T. Evans; 15. Remote sensing of primary production in the ocean: promise and fulfilment T. Platt, S. Sathyendranath and A. Longhurst; Part V. Future Challenges: 16. Beyond JGOFS K. L. Denman and M. A. Pena; Part VI. Conclusion: 17. Some conclusions and highlights of JGOFS mid-project achievements J. G. Field, H. W. Ducklow and R. B. Hanson.