A unified classification of alien taxa based on the magnitude of their environmental impacts has been developed in response to these issues. EICAT (Environmental Impact Classification for Alien Taxa) is a simple, objective and transparent method for classifying alien taxa in terms of the magnitude of their detrimental environmental impacts in recipient areas. Based on evidence on the impacts they have been causing on native taxa in their introduced range, alien taxa are classified into one of five impact categories. Each of these five impact categories represents a different impact magnitude, depending on the level of biological organisation of the native biota impacted (individual, population or community) and the reversibility of this impact.