An "invasive species" is defined as a species that is

1) non-native (or alien) to the ecosystem under consideration and

2) whose introduction causes or is likely to cause economic or environmental harm or harm to human health. (Executive Order 13112).

Invasive species can be plants, animals, and other organisms (e.g., microbes). Human actions are the primary means of invasive species introductions.

Invasive Species Definition Clarification and Guidance White Paper (PDF | 104 KB)
Submitted by the Definitions Subcommittee of the Invasive Species Advisory Committee (ISAC), Approved by ISAC Apr 27, 2006.

On Invasivespeciesinfo.gov you can learn about the impacts of invasive species and the Federal government's response, as well as read select species profiles (animals, aquatic species, microbes, and plants) and find links to agencies and organizations dealing with invasive species issues.