A major step in tackling invasive alien plants consists of identifying those species that represent a future threat to managed and unmanaged habitats. The European and Mediterranean Plant Protection Organization reviews and organizes data on alien plants in order to build an early warning system. A prioritization system is being developed to select species that represent emerging threats and require the most urgent pest risk analysis to implement preventive measures and to perform eradication and management measures. Attention has been drawn to the Mediterranean Basin which is particularly vulnerable because its climatic conditions potentially allow the establishment of sub-tropical and tropical species. Surveys and rapid assessments of spread and impact have allowed identification of emerging invasive alien plants for Mediterranean countries: Alternanthera philoxeroides (Amaranthaceae), Ambrosia artemisiifolia (Asteraceae), Baccharis halimifolia (Asteraceae), Cortaderia selloana (Poaceae), Eichhornia crassipes (Pontederiaceae), Fallopia baldschuanica (Polygonaceae), Hakea sericea (Proteaceae), Humulus japonicus (Cannabaceae), Ludwigia grandiflora and L. peploides (Onagraceae), Hydrilla verticillata (Hydrocharitaceae), Microstegium vimineum (Poaceae), Myriophyllum heterophyllum (Haloragaceae), Pennisetum setaceum (Poaceae), Pistia stratiotes (Araceae), Salvinia molesta (Salviniaceae), Solanum elaeagnifolium (Solanaceae). These species represent priorities for action. Some other species are placed on the observation list, as available information does not allow them to be counted among the worst threats: Akebia quinata (Lardizabalaceae), Araujia sericifera (Apocynaceae), Delairea odorata (Asteraceae), Cabomba caroliniana (Cabombaceae), Nassella neesiana, N. tenuissima and N. trichotoma (Poaceae), Sesbania punicea (Fabaceae), and Verbesina encelioides (Asteraceae).