Impacts of biological invasions on recipient plant communities vary enormously, depending on both the traits of the introduced species and those of its new ecosystem. The trajectories of many introduced plant species in invaded ecosystems seem very similar to those taken by native plants as part of secondary succession. It is likely that studying them in the framework of modern succession ecology would be fruitful. Other introduced species of plants, animals and pathogens cause massive, rapid and often irreversible changes in the recipient communities, of a magnitude rarely produced by native species. Understanding such invasions, and the great range of impacts caused by introduced species, will probably require at least some approaches different from those of other sciences of vegetation change. Although invasion biology has been somewhat dissociated from other research on vegetation change, at least a partial rapprochement is underway, and, in any event, it is not evident that understanding of invasions has been retarded by the dissociation. Research on plant invasions has already contributed greatly to recent progress in understanding the determinants of community structure and function, as well as to many other areas of ecology. The rapidly increasing number of communities composed wholly or largely of introduced species would seem to be an ideal probe into questions about the nature of plant communities and the forces molding them, but they have barely been exploited in this regard. Invasion biology has not produced powerful general laws, but neither has community ecology as a whole. This fact does not indicate that they are weak sciences, only that any laws in these fields will probably be local, contingent patterns because of the complexity and idiosyncrasies of biological communities.