Knowledge of characteristics helpful in screening potential invaders and in elaborating strategies to limit their success is highly desirable. We focused on gammarid amphipods from Western Europe and North America to discover biological and/or ecological traits that may explain successful invasion by these species. Two typologies were considered: an analytical one, with groups built on the basis of biological or ecological similarities, and an empirical one, with groups constituted a priori according to a species’ invasive status and its fresh or brackish water origin. The results obtained are discussed in the light of three hypotheses that may influence invasiveness: biotic potential, species size and euryoeciousness. The analysis revealed a particular ecological profile for invaders, with a strong influence of salinity tolerance, but no typology was found based on biological characteristics. Invasiveness cannot be predicted from a limited number of criteria, and is the result of a combination of several characteristics. Invasive species therefore exhibit a particular ecological profile rather than a biological one, contrary to most classical explanations.