All non-European nationals (with certain exceptions) who come to work (and live) in Belgium, have to apply for and obtain a work authorisation before they start working.
Self-employed professionals must apply for a professional card (Carte professionelle or Beroepskaart), whereas employees will have to apply either for a work permit (before applying for residence) either, since January 2019, for a single permit (for authorisation of both working and residing) depending on the situation. Despite the latest introduction of the Single Permit, the conditions for the unlimited work permit (ex work permit A) and limited work authorization for foreign nationals in precarious conditions (ex work permit C) remain unchanged.