A proposed comprehensive typology of factors and their interactions (represented by intersections in the Venn diagram) that explain invasions: Alien species traits, Location characteristics, and Event-related factors. Intersections between two (or all) these main classes of factors denote situations where their combinations determine invasions, e.g. the climate at a location needs to match the niche requirements of the alien to result in a successful invasion. For a successful invasion, all factor classes and their interactions need to be favourable (Species × Location × Event), i.e. a species with suitable traits is introduced to a suitable habitat in a region with matching climate and the propagule numbers arriving during that introduction event are enough to allow for successful establishment, possibly resulting in invasion.