We inhabit the blue planet, but our knowledge of life underneath the blue surfaces of the ocean remains surprisingly limited. In reality, investigations of marine life have just begun, and it is only now, when we can utilize custom-built research ships and the finest modern technology, that we can learn how ecosystems in the oceans are structured and function. The research programme Census of Marine Life seriously addresses this situation and challenges marine biologists to utilize the most advanced technology to achieve true new information in areas of the ocean that were poorly studied previously. The project MAR-ECO, an element of the Census of Marine Life, rises to the challenge and investigates the diverse animal life along the vast underwater mountain chains of the open ocean. MAR-ECO is an international research project in which scientists from 16 nations take part. Norway, represented by the Institute of Marine Research and the University of Bergen, co-ordinates the project which will enhance our understanding of occurrence, distribution and ecology of animals and animal communities along the Mid-Atlantic Ridge between Iceland and the Azores. The Mid-Atlantic Ridge is the volcanic mountain range in the middle of the ocean, marking the spreading zone between the Eurasian and American continental plates. New ocean floor is constantly being formed, and Iceland and the Azores are volcanic islands created when the mid-ocean ridge breaks the sea surface. The fascinating groups of animals to be studied are fishes, crustaceans, cephalopods (squids) and a wide range of gelatinous animals (e.g. jellyfish) living either near the seabed or in midwater above the ridge.