Are the borders open? Yes, but travel to high-risk “red” areas is banned.
Do arrivals have to quarantine? A 14-day quarantine is mandatory for people arriving from areas listed as high-risk (marked red), to which Paris was added in August. A quarantine is recommended for travelers from areas marked orange, meaning there’s an increased risk. Find the full list here.
Are there any other entry requirements? People traveling from a red area have to do a test upon arrival. A test is recommended, but not compulsory, for people traveling from orange areas. From August 1, all travelers who intend to stay in Belgium for at least 48 hours (and have been abroad for more than 48 hours) have to fill out a so-called Passenger Locator Form before their arrival.
What about travelers from outside Europe? Non-essential travel to and from outside Europe is not allowed. Arrivals have to get a test and quarantine.
Find out more: https://diplomatie.belgium.be/en
European Centre for Disease Prevention and Control: https://www.ecdc.europa.eu/en/covid-19-pandemic