The theme for the International Day on Biological Diversity (IDB) in 2009 is invasive alien species (IAS) - one of the greatest threats to biodiversity, and to the ecological and economic well-being of society and the planet.

Designation of IDB 2009 on the theme of invasive alien species provides Parties to the Convention on Biological Diversity (CBD) and those dealing with IAS, opportunity to raise awareness of the issue and increase practical action to tackle the problem.