International trade is one of the most important pathways for both the intentional and the unintentional introduction of alien species. The intentional introduction of alien species takes place through the importation of exotic plants and animals as commercial products. But alien species may also enter unintentionally, as byproducts of trade, e.g., through cross-breeding of exotics with local populations, as parasites of products, e.g., as an infestation or infection on agricultural products, or as "stowaways" during trade, e.g., in the ships, planes, or vehicles that deliver products. Furthermore, the unintentional introduction of alien species occurs not only by way of trade in goods, but also by way of trade in services, e.g., as parasites or stowaways through tourism. Not surprisingly, governments have used their authority and responsibility to regulate commerce at their borders as a primary means of controlling the introduction of alien species. As the volume and geographical spread of trade grows, this regulatory challenge will increase, particularly for developing country governments.

This Article examines the potential interaction between the policy objectives and rules associated with efforts to regulate the introduction of alien species, and those designed to promote and protect free trade. Free trade rules, as represented by the agreements of the World Trade Organization (WTO), generally recognize the right of governments to impose rules necessary to protect domestic animal and plant life and health. However, WTO rules may not take full account of the specific concerns of officials and nongovernmental organizations (NGOs) working to protect native biodiversity from the threat of invasive alien species.