This book includes the 21 invited talks of the symposium "A Marine Science Odyssey into the 21st Century" (36th European Marine Biology Symposium), held in Maó, Minorca (Balearic Islands), from 17 to 22 of September, 2001. The authors of these papers and the other participants joined around Prof. Margalef to discuss together his ideas, that have been a source and a challenge for a great ecological synthesis and have opened new ways to relate ecology with evolution and other disciplines for more than half a century. This collection of papers, written by several of the world's leading marine and terrestrial biologists, evolutionists and ecologists, physical and chemical oceanographers, limnologists and geologists, makes this book a reference text for the new decades. The papers provide numerous ideas, suggestions and recommendations for the study of the seas and oceans. This book is mainly addressed to the new young generations of scientists interested in understanding, in a wide view, the functioning of the aquatic ecosystems and to deepen in the processes that should be taken into account to preserve their extant biodiversity.