Amphipods are found in almost all aquatic environments, from beach level down to deepest trenches. About 80% of the total amphipod species diversity live in the marine environment and are the most common crustacean order in most deep sea regions. Considering threats to biodiversity, new knowledge of existing species and discovery of undescribed species from existing long-time collections and the subsequent study are urgently required. This special Issue on marine Amphipoda was inititated during the IceAGE amphipod determination workshop in the frame of the IceAGE project (Icelandic marine Animals: Genetics and Ecology) and invites amphipodologists worldwide to contribute with their work.