Members of any other EU countries may enter Belgium without the need to obtain a visa. There is no limit on the amount of time they may remain in the country but they will need a residence permit if they decide to stay longer than three months.
Belgium is also a Schengen country which allows free movement from any other Schengen nation without any further visas required.
Visitors from outside the EU can enter the country on a short-term basis if they are from a select list of countries such as the US, Canada and Australia. Visitors planning a longer stay, or coming from other countries will need a Schengen visa.