Non-native species are a major cause of the loss of biodiversity globally and their impacts are especially severe on the island ecosystems and species typical of our Overseas Territories and Crown Dependencies. The biodiversity found in the Territories contains many globally threatened and endemic species and also populations of species whose abundance is of regional or global significance. This study was comissioned to investigate, through desk study, the occurrence of non-native species in the Overseas Territories and Crown Dependencies of the United Kingdom.