Terrestrial life likely comes first from water. Aquatic systems (marine and freshwater), which cover about 70% of Earth’s surface, play fundamental roles in ecological equilibria of our planet. Aquatic species are all living in close associations, forming complex networks that determined ecosystem’s stability and production. Beside this ecological relevance, species involved in such symbiotic interactions and even the nature of these associations are still poorly known. Objectives of this web site are 1) to make an inventory of known symbiotic associations in aquatic systems thanks to the contribution of experts, specialists of taxonomic groups, and 2) provide pedagogical documents required for a better comprehensive view of all of these symbiotic associations.