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The invasions of introduced species into five reserves in tropical savannas and dry woodlands are described. Vascular plants are the group having the most introduced species; invasions are least important in dry, regularly burned savannas, more important in moist, derived savannas (where scrambling shrubs are invading) and most important in wetlands (where trees, shrubs, herbs and aquatic macrophytes are invading). Control, which should be initiated early in an invasion, is being implemented for only a few species. Water-dispersed plants and herbaceous weeds are generally impossible to control using current technology. Biological control measures are urgently required for some invasive shrubs (e.g. Chromolaena odorata). Introduced vertebrates are generally less important, but exceptions are large mammalian herbivores in Australia and several near-native ungulates in southern Africa. Predation apparently limits the number of successful vertebrate invasions. Introduced mammalian pathogens have had severe ecological effects in Africa. Invertebrate invasions require more research.