Successful colonization of a new location involves a fourstep process: departure from the source, dispersal across a barrier, establishment, and range expansion in the new region. The hurdles at each step mean that a restricted subset of potential source species become established in the new location (Whittaker and Fernandez-Palacios 2007). Further, among the species that do successfully colonize, these same four hurdles result in genetic differentiation from the source (Lee 2002; Gilchrist and Lee 2007). Taking advantage of the many human-aided invasions throughout the world, a massive research program now focuses on the third and fourth stages of the colonization process (i.e., establishment and range expansion in the new location). Several book-length reviews on these stages have recently appeared (Sax et al. 2005; Allen and Lee 2006; Gilchrist and Lee 2007; Lockwood et al. 2007; Nentwig 2007). New Zealand has been particularly affected by invasive species (Allen and Lee 2006), and in the classic volume Genetics of Colonizing Species, Wodzicki (1965, p. 456) noted that it “offers an excellent opportunity to study the results of a large scale introduction of exotic species and their adaptation to a new environment.” The 2007 American Society of Naturalists symposium in New Zealand therefore seemed an ideal setting to discuss advances in the genetic changes underlying invasion. We asked contributors to this symposium to focus on original research, covering the spectrum of all four stages of the colonization process.