Based on the current spread of exotic mosquito species (EMS) in Europe, on the number of interceptions in Belgium and on suitability models developed for Aedes albopictus (Skuse) in Europe, EMS are likely to establish and spread in Belgium. A prerequisite for their control is their early detection. Therefore, the Belgian federal authorities and the federated entities fund a three-year active monitoring project (MEMO) (July 2017 June 2020). The aims are early detection of EMS in Belgium, quantifying locally established EMS populations, evaluating the EMS import risk at possible points of entry (PoE), expand reference collections and make recommendations for a future, long-term, cost-effective EMS monitoring plan in Belgium. Monitoring activities are implemented at 23 PoE using adult trapping with CO2 and lure traps, egg sampling with oviposition traps and larval sampling with dippingnets. DNA-barcoding is used by BopCo to validate morphological identifications and to expand the DNA reference database. Specimens are also added to the morphological reference collection at RBINS. Since July 2017 four EMS were intercepted. The colonised area of Aedes koreicus (Edwards) in Belgium increased from 7 to 113 km². Aedes japonicus (Theobald) was detected again in southern Belgium from where it was thought to be eliminated. This species was now also collected at the border with Germany. Anopheles pharoensis (Theobald) entered Belgium via cargo transport. Aedes albopictus was intercepted at four PoE. To conclude, EMS are effectively entering and spreading in Belgium, and appropriate control management strategies on the national level are urgently needed.