Significance Our ability to predict the identity of future invasive alien species is largely based upon knowledge of prior invasion history. Emerging alien species—those never before encountered as aliens—therefore pose a significant challenge to biosecurity interventions worldwide. Using a global database of the first regional records of alien species covering the years 1500–2005 we detected a surprisingly high proportion of species in recent records that have never been recorded as alien before. The high proportion of these emerging alien species mainly resulted from the increased accessibility of new source species pools in the native range. Risk assessment approaches that rely less on invasion history will need to be prioritized.