The stabilization and isolation of highly reactive species has long been the subject of chemical research. This review will focus on a large and important class of reactive species that has only recently received considerable attention: lowvalence element heterocycles of the group 13 and 14 elements. The unifying feature of these species is the bifuntionality at the element center, which has a lone pair of electrons and a formally vacant I?-orbital. Therefore, these species can display not only the expected electrophilic reactivity of other low-valent species but also nucleophilic reactivity at the element center. It is, in fact, this unique reactivity that is the focal point of this review because, while these species are fundamentally important to a broader understanding of main group chemistry, their reactivity should also lead to applications in synthetic and materials chemistry, catalysis research, and perhaps beyond. The reactivity described in this review not only summarizes what has been done but also highlights the potential of these species.