What does the Belgian single permit actually combine?

Belgium's single permit merges the work permit and the residence permit into one combined authorisation. As the Immigration Office puts it, applying for the work permit is equivalent to applying for the residence permit – the decision is a single administrative act covering both.

The single permit is required for third-country nationals who will stay and work in Belgium for more than 90 days. Both the competent region and the Immigration Office jointly evaluate the application, which is why it brings labour and immigration checks together in one process.