Here, the same rules apply as for residents but with a few exceptions.
Individuals who earn an income in Belgium and are not residents need to pay tax, whether the income comes from a full-time job, self-employment of renting out a house or apartment. The tax will only be calculated on income earned in Belgium.
Some employees are taxable according to the “special tax rate for foreign executives” (NL: bijzonder aanslagstelsel voor buitenlandse kaderleden FR: régime fiscal particulier des cadres étrangers). This is only applicable if the executive has been sent to Belgium or hired abroad and will work in Belgium for a limited period. This system was designed so foreigners can receive an amount of non-taxable money to pay for extra costs incurred due to moving to Belgium. These costs need to be justified, so you need to keep all receipts and evidence for these additional costs.
It is possible that you earn an income in Belgium AND in your home country. This means that you would have to pay taxes on certain income twice (since it’s a general rule that in the country where you live, you pay taxes on your worldwide income, not just the income from that country). To prevent this happening, there are rules to prevent double taxation. Belgium has treaties with over 50 countries and a full list can be found on the website of the Administration of Fiscal Affairs (http://fiscus.fgov.be/interfafznl/nl/international/conventions/index.htm).