When is a tax treaty concluded?
The Netherlands has concluded a tax treaty with many countries to prevent you from paying tax more than once on your income or assets. All tax treaties can be found at rijksoverheid.nl.
If the Netherlands has not concluded a tax treaty with a country, the 'Besluit voorkoming dubbele belasting 2001’ (Double Taxation (Avoidance) Decree 2001, only available in Dutch) applies.
The tax treaties do not contain any rules for the levying of national insurance contributions. Read more about this at Social security for cross-border working and entrepreneurship.