Besides habitat fragmentation, the introduction of invasive species is considered to be one of the greatest threats to global biodiversity. Due to increased global trade, habitat degradation and climate change the number of species introductions has increased spectacularly during the last decades. This has led to changes in structure and functioning of ecosystems worldwide. In this study, the impact and spread of alien macroinvertebrates in surface waters in Flanders was investigated. To this end, a large database consisting of biological and physical-chemical data was used, which was collected by the Flemish Environment Agency and supplemented with own sampling campaigns. An integrated approach was aimed for, where the results from laboratory studies, long-term field data analysis and data-driven modelling were combined in order to gain insight in the ecology of alien macroinvertebrate species and the drivers that cause changes in macroinvertebrate community composition. A detailed study on the distribution of alien macroinvertebrates in Flanders revealed that in total, 65 alien macroinvertebrates are established of which 40 are regularly encountered in fresh and slightly brackish inland waters. Most alien taxa belonged to the crustaceans and molluscs originating from North America and the Ponto-Caspian region. Many alien species were first discovered in the east of Flanders from where they started the colonisation of the central and western parts of Flanders. Changes in the macroinvertebrate composition were discovered during the last two decades as a result of changing environmental conditions and the introduction of alien species. When analysing the factors that favoured the establishment and spread of alien macroinvertebrates it was found that shipping, hydro-morphological and physical-chemical factors were detrimental for the success of alien macroinvertebrates. Canals, harbours and the polder waters were hot spots for alien species introductions. Small streams were less invaded by alien macroinvertebrates ...