Since 2000, I’ve been studying how one avian species, the house sparrow, has managed to colonize most of the planet. Through long-term work in Panama and Kenya and other studies in Senegal, Vietnam, Australia, Argentina, and several sites across Europe, my students, colleagues and I have found that particular changes in the behavior, stress physiology, and immune defenses of individual sparrows affected their ability to colonize new areas. Most recently, we have begun to study epigenetic processes underlying invasions, as one form of epigenetic variation (DNA methylation) is instrumental to the phenotypic plasticity that is so important to the success of some invaders. Over the last ~10 years, we have found that part of the reason that the house sparrow might be such a pest is its propensity to use DNA methylation to sculpt its physiology and behavior to local conditions. In particular, we find that the genomic substrates for epigenetic variation, something we’ve termed epigenetic potential, seem to have been especially important in range expansions of this species.