Once an exotic species has successfully established a self-sustaining population, it may spread beyond its initial point of introduction and establish meaningful interactions with species native to this location. This chapter reviews the relatively large literature on models of geographic range expansion (spread) in invasive species. In particular, it notes the tremendous bias towards a few, very successful and widespread exotic bird species, on our understanding of exotic species range expansion. For the same reasons that exotic birds have already contributed to understanding invasions (i.e., there is detailed information on their numbers and locations), it is argued that with the right research effort they can also help us gain a clear picture of why some exotic species do not expand their ranges once established, or only do so after a long lag period.