Hydrothermal communities of various species compositions have been described from the eastern and western Pacific and Atlantic. Brine and cold seeps and hydrocarbon seepages have been found off Florida, off the Oregon and Japanese subduction systems, on the Laurentian Fan, near Barbados, and off Louisiana. Biomasses range from 10 to 70 kg/m super(2), fresh weight. Basic microdistribution of species groups in aureoles centered around hydrothermal vents reveals different levels of adaptation to harsh physico-chemical conditions. Two groups of primary producers can be recognized: a highly efficient cool water group with large vestimentiferan tube worms and bivalves, and alvinellid polychaetes adapted to hot waters. Both groups are exploited by specific carnivores. The food web is based on sulfooxidizing symbiotic bacteria. Methanotrophic symbiotic bacteria have recently been found in bivalves off Louisiana. Nearly 160 species new to sciences have been described, with an abnormally large number of panchronic species. The short life span of hydrothermal vents together with the world-wide distribution of several species raise questions of propagation and colonization.