Background Invasive alien species are a major threat to native biodiversity; competing with native species for food and habitat. Associated problems include reductions in the populations of native species and decreased genetic diversity. Non-native species can also act as reservoirs of infectious diseases that can lead to the extinction of some rare or endemic (not found elsewhere) species. Objectives This LIFE+ Biodiversity project’s global objective is to halt the loss of biodiversity associated with invasive alien species on the Iberian peninsula, thereby contributing to the aims of the European Commission’s strategy for "Halting the Loss of Biodiversity by 2010 and Beyond" [COM (2006) 216 final]. Involving cooperation between Spain and Portugal, this is the first trans-boundary project launched in the EU to tackle invasive alien species. Expected results: 1. Approval of specific legislation to enforce the national Catalogue of Invasive Alien Species; 2. An Iberian Action Plan to combat invasive alien species; 3. The establishment of an Iberian Working Group on Invasive Alien Species; 4. A ban on the trade and sale of exotic pets; 5. Accurate information on invasive species, and their presence and distribution within the Tajo and Guadiana river basins.