Invasion of long-established ecosystems by organisms is a natural phenomenon, but human-facilitated introductions have greatly increased the rate, scale, and geographic range of invasion. For millennia, humans have served as both accidental and deliberate dispersal agents, beginning with our earliest migrations, accelerating in the age of discovery, and accelerating again with international trade. Notable examples of invasive plant species include the kudzu vine, Andean pampas grass, English ivy, Japanese knotweed, and yellow starthistle. Animal examples include the New Zealand mud snail, feral pig, European rabbit, grey squirrel, domestic cat, carp, and ferret. Some popular reference sources now name "Homo sapiens", especially modern-age humans, as an invasive species, but broad appreciation of human learning capacity and our behavioral potential and plasticity argues against any such fixed categorization.