Some alien species have been deliberately introduced to Norway, while others have escaped from cultivation or captivity, or been unintentionally introduced with shipping, road vehicles or other means of transport or with goods from other parts of the world.

Others again have been brought along as "hitchhikers" on species that have been deliberately introduced. Most organisms arriving in a new environment are unable to adapt, and therefore die out. Others are able to establish themselves, and many of these prove to be harmful to ecosystems and property; they may also cause problems for agriculture and other activities or pose a health risk. They are known as invasive alien species.

Norway is seeking to prevent the introduction and spread of invasive alien species. The Strategy on Invasive Alien Species, published in 2007, makes it clear that all relevant sectors share the responsibility for managing alien species.

The 2007 Norwegian Black List of alien species lists 2 483 alien species known to occur in Norway. It presents ecological risk analyses for 217 of these, 93 of which are considered to represent a high risk to Norwegian ecosystems and are classified as invasive alien species.