Humans have moved countless of species throughout the world, hastening their spread. Invasive species endanger aquatic ecosystems because of challenges to biodiversity and human demands for water supplies. This chapter investigates status, impact and characteristics of aquatic invasive species (AIS) and raises new questions. It analyses the effects of AIS, factors that limit their spread; the natural and anthropogenic role in the dispersion of AIS. It also analyses the traits of species that offer the greatest threat to future invasions, as well as those that prepare the path for subsequent invasions. The research also looks at the relationship between species invasions and other human consequences including climate change and landscape modification. It finishes by exploring the way forwards in the field of AIS biology.