Abstract: The invasion of alien species that are morphologically indistinguishable, or hardly distinguishable, with the native species or earlier established species is regarded as cryptic invasion. This kind of invasion is often undetectable by human beings. The types of cryptic invasion include invasion of the alien sibling species, genetic lineages, geographic populations, and a hypothesized “back introduction”. These alien species are more readily hybridize or introgress with native species or earlier established species and thus result in the long-term ecological effects on the invasive species or native species. The research related to cryptic invasion should be further strengthened in view of its widespread occurrence．

Key words: Biological invasion, alien species, invasion mechanisms, cryptic invasion, sibling species, genetic lineage, back introduction