The native flora of Réunion Island in the Indian Ocean is threatened by invasive woody plants introduced for agriculture, forestry or as ornamentals. We reviewed archives to identify woody plants introduced since colonisation and ranked the biological impact of the main non-indigenous species on native vegetation. The relationship between cumulative number of non-indigenous plants and population follows an s-shaped curve, but the rate of introduction was mainly determined by historical periods with five main introduction phases identified. A total of 318 introduced woody species were recorded with 132 identified as naturalized in natural ecosystems. Of these, 26 of the more serious invasive species (i.e. having a large biological impact on the new environment) were selected and ranked by biological impact to native ecosystems. Hiptage benghalensis, Ligustrum robustum var. walkeri, Acacia mearnsii, Ulex europaeus and Psidium cattleianum were identified as having the highest invasiveness capacity and the greatest impacts on succession and utilization of resources in natural areas. A strategy is required to manage high-priority invasive species and reduce the rate of non-indigenous plant introductions to the island.