Hybridization is thought to have played an important role in shaping the evolutionary history of diverse island taxa. Yet secondary contact doesn’t always result in introgressive hybridization, and it is important to understand what determines the ecological and evolutionary outcomes of secondary contact, particularly in the face of widespread secondary contact between island endemics and recently introduced species. While there are reasons that secondary contact commonly leads to heterospecific mating on islands, the consequences of secondary contact will differ depending on the nature of the species involved. I will present the results of our field work on introduced and endemic species of the plant Psidium (guava) on the Galápagos Islands of Ecuador, exploring the role of secondary contact in the ongoing extirpation of the endemic species. I will then discuss the results from a quantitative analysis of published empirical research on secondary contact among vertebrate, invertebrate, and plant species on the five most well-studied remote oceanic archipelagoes. This analysis suggests the relative importance of different factors driving secondary contact and heterospecific mating, such as disturbance, inter-island dispersal, and compromised assortative mating. I will discuss the hypothesis that introgression is a more common outcome between island endemic species while reproductive interference is a more common outcome between endemic and introduced species, as well as the contention that reproductive interference between endemic and introduced species is a cryptic threat to the conservation of island endemics.