If you come to Brussels to work for an EU institution or an International organisation, specific rules apply as you will generally not be subjected to the belgian system in terms of social security and taxation. However you still will need to register in Belgium !
Regarding Social security , officials and other servants of the European Union (and members of their family subject to certain conditions) are covered by the Joint Sickness Insurance Scheme of the European Union (JSIS), which reimburses medical expenses for most medical procedures or treatments at the rate of 80-85% (subject to certain ceilings).
Regarding taxation, click here.
To know how to obtain a belgian residence permit click here.
There are a number of ways in which people can come to work in the Institutions : permanent officials, parliamentary assistants, contract staff, temporary staff, seconded national experts…
For information on careers, including recruitment, promotions, pay and benefits see the Staff Regulations.