Invasive species are a relentless problem—there will always be more species that can arrive on our shores and whose impact on our economy and environment is difficult to predict. However, there are some dangerous species whose establishment we know would disrupt natural ecosystems and cause tremendous damage to resource-dependent economies like agriculture, forestry, and fishing. The ten species described below are ones we definitely do not want and are prime examples of why we must increase efforts to prevent new introductions. We must take immediate precautions now to insure that in 10 years we can report the good news that these looming arrivals, and many others like them, have been kept at bay.